So this is an issue I have been thinking about for a while. Both in the fantasy world I'm making and in many examples of fantasy media magic users are able to bring in new amounts of physical matter into the world. For example ice wizards in Warcraft launch shards of ice out of thin air to attack enemies, a Final Fantasy mage creates a crystal shield, druids/plant mages make plants grow out of the ground or their hands, a nasty goblin warlock conjures acid out of his mouth, etc. Logically, wouldn't the world eventually fill up with new matter from mages using generic spells such as these until people literally run out of space to live? How could I avoid this issue while still having a magic system that allows the creation of new matter as depicted in fantasy media such as the examples I listed? Let's further assume that launching things off into space is not an option.
Something I came up with is that my world has an ambient "mana field" (similar to how the real world earth has a magnetic field) that takes magically created objects and slowly converts them into ambient mana (effectively destroying them from a physical perspective).
Are there other options for dealing with this issue? Or a way for me to improve my idea? I'm hoping for a solution that would be as inconspicuous as possible, ideally something that would take centuries to notice is happening on a large scale, and for most practical purposes is indistinguishable from a world without such a process.
Also, I'm hoping for a solution that would still make it possible to keep magically created items around indefinitely, ideally through completely mundane means. I was thinking for example that my mana field would be linked to natural processes such as weathering and erosion, meaning that you could theoretically keep a magically created item around forever if you maintained it by keeping it clean and making sure it's not exposed to the elements for long periods of time without maintenance.
One last thing, I couldn't seem to find any other examples of people asking this question or something similar, even in places like this dedicated to worldbuilding. Is it possible that maybe I'm overlooking something really obvious to most people that would render my dilemma a non-issue?
Edit for clarification: I'm not asking about specific item summoning spells or "magic-item hoarders" or similar. I'm asking about an aspect of magic in general as seen in fantasy media such as books, games, etc. For example, in the game Skyrim there are spells such as ice bolt that launches a shard of ice created out of thin air, or say a generic fantasy druid that makes plants grow to enormous sizes. Logically, wouldn't the world eventually run out of space from mages using generic spells such as these?
The solution I'm looking for is more something along the lines of some aspect of the world or a law of "physics"/magic. The best solution in the context of this question is something both effective and also importantly inconspicuous, as in as similar as possible to a world without this solution/magical law/etc, meaning that constantly creating "bags of holding" or pocket dimensions for storage probably don't fit.
The "ambient mana-field" I came up with and listed as a solution is an example of what I meant. Does this make sense as a solution? Or are there better solutions (better here meaning more inconspicuous while still effectively solving the issue) or a way to improve it?
Edit 2: Reading this https://tvtropes.org/pmwiki/pmwiki.php/Main/ElementalBaggage is part of what inspired the questions. I noticed a lot of you brought up conservation of mass. Once again I want to emphasize that I really appreciate everyone's help here, but I'm highly doubtful that conservation of mass could be at play in many of these cases. For example, the idea of using water vapor from the air to create ice, the issue is that there's only so much water vapor in a given area. In order to do the kind of feats someone like Iceman or a fairly typical fantasy ice mage does they would need to be drawing in water vapor from literally miles away, but they're almost always depicted as not being able to manipulate their element much further than a couple hundred yards away or so, if that. And that doesn't even get into cases where they're inside somewhere, like a building or dungeon, in which case they would need to draw in water vapor literally through the walls. Not to mention that this much matter being drawn in to one location logically would be easily visible. So if for example Iceman was drawing in water from the air for his power it would look like a huge cloud of mist (aka water vapor) suddenly gathering to him. Something like creating a block of ice would require enough water vapor to fill a large auditorium. Same thing applies to other examples like dust in the air for rocks or carbon for crystals etc.
Edit 3: Just for clarity and emphasis, I'm specifically asking for something "inconspicuous" (as in as similar as possible to world without such a solution while still solving the problem) and more specifically if there is a way to improve my idea to make it more inconspicuous assuming it’s effective in the first place or if there’s a better (more "inconspicuous") solution. Such a solution would ideally allow someone to keep magically created matter around indefinitely through completely mundane means, such as in my example where the absorption back into mana is tied to natural processes such as weathering, erosion, evaporation, decay, etc, meaning that you could theoretically keep a magically conjured object around indefinitely by maintaining it by doing things such as cleaning it, not leaving it exposed to the elements for long stretches of time without cleaning and maintenance, etc. essentially exactly the same way you would maintain a mundane object and keep it from breaking or eroding away, etc.
In other words, how can I solve this issue while still leaving the world in as similar a state as possible to a world without such a solution?
Edit 4: As I mentioned, I already came up with an idea of my own on how to deal with this issue, and I'm mainly hoping for feedback in regards to its viability (hence the reality-check tag) and if there's a way to improve it by making it even more inconspicuous. I'm not really hoping for people to come up with completely different solutions unless they better meet the criteria (effective and inconspicuous, as little difference from a world without the solution as possible) then the idea I already came up with, for example, as I mentioned is there perhaps something really obvious most people take for granted that I'm overlooking?
Edit 5: Some people brought up the size of the earth and that it would hundreds of thousands of years for this to happen. The problem is that this still makes it an issue in fantasy. Timescales of tens or even hundreds of thousands of years are not at all unheard of in fantasy, some stories such as the Wheel of Time series (I'm not asking about the Wheel of Time, I'm just using this as a random example that hopefully some people are familiar with to better explain what I mean) even feature feature worlds that had been around for possibly eternity, with civilizations going through cycles of rising and collapsing. The fact that it would take a long time to happen doesn't solve the issue, because it would still happen at some point. This would particularly be an issue for my story because I am in fact planning on having long-lost civilizations from thousands or even millions of years ago in my story, with some of the oldest ones having a very "Lovecraftian" element to them.
Edit 6: Great job guys! I'm loving the suggestions! One change I decided to implement was to change my "mana-field" idea into a "Matter Absorption Field" basically the same idea except that instead of converting magically created matter into mana it simply absorbs it into nothing (destroying it in other words). The reason for this is that as Vilx- mentioned, all that extra mana could cause problems.
Edit 7: This is just a modified version of my solution made in response to the comments and suggestions here. I thought it would be better to just repost it instead of going back and changing the original statement, not to mention that having the previous version easily visible could be helpful in answering the question. Once again I would very much appreciate feedback in regards to its viability as well as how it could be improved to be as inconspicuous as possible. Or maybe you have an alternate, better solution that better meets the criteria of effectiveness and inconspicuousness.
-My Idea: I have an idea of my own that I'm planning on using in a story I'm writing. It involves a "matter absorption field" (similar to how the real world earth has a magnetic field) that slowly absorbs magically created matter essentially into nothing. It would work through natural processes such as weathering, erosion, evaporation, decay, etc. Meaning that this would usually be too slow to notice at first and that theoretically you could keep a magically created object around indefinitely as long as you maintained it by keeping it clean, making sure it's not exposed to the elements for long periods of time without cleaning and maintenance, etc, basically exactly the way you would maintain something in the real world through perfectly mundane means.
For instance you could keep a magically created sword around forever by maintaining it using exactly the same mundane methods you would use to maintain a normal sword, by cleaning it, making sure it doesn't rust, etc, no special enchantments needed. However if it gets abandoned in a field it would most likely rust and weather away and thus be absorbed by the "matter absorption field".
This also means that you could still have magically created objects from thousands of years ago still be around because they were somehow well preserved, similarly to how in the real world we still have some things like swords and buildings from thousands of years ago long after most of their contemporaries rusted and eroded away.
Also this means you could still have things like a mage creating a building from magically conjured stone, and not worry about it suddenly disappearing into nothing without warning, as long as they don't abandon it and occasionally maintain the building just like people in the real word do.
Lastly you wouldn't need to worry about magically created food or water suddenly disappearing right out of someone's stomach, or worse their bloodstream or brain, and it would only be absorbed into the field when it leaves the person's body and starts evaporating, decaying, etc.
Also, I think this solution could potentially work in pretty much any pre-existing setting and not change anything noticeable about the story or setting (this last part doesn’t matter much if at all and can be freely ignored, all that really matters is that my idea works for my setting, this is just a random observation on my part).
Edit 8: I just realized that buildup of extra heat from the magical energy could be an issue as well, in which case absorption of extra ambient heat originating from magic energy use could be a feature of my field as well. Also I know that the name I thought of is very awkward, so I thought of changing the name to a “homeostasis field” as that is essentially what it does, helping maintain a certain set of conditions on the planet, i.e. the planets homeostasis.