Disclaimer: I know very little about climate science with reference to geological formations. All the answers I'll give you are based on my immediate research (i.e. I am googling as I go because I like this question). As a result of that, this will read a lot like a stream of consciousness.
Firstly, I'd like to outline this chunk of land as being divided by 2 tectonic plates - T1 and T2. T1 encompasses all of A, most of C, part of D1, T2 being everything south of that.
Let's start with D1 first: mountains are formed as tectonic plates rub up against each other. It is possible that this part of the island was caused by the collision of 2 different islands. According to this link, the Alps were created by "the subduction of this basin [Tethys Ocean, an ancient ocean between Europe and Africa] and the collision of Africa with the Eurasian plate is what caused the formation of these mountains". If we want to relate to Tibet, as you referenced in your question, that was caused by the Indian subcontinent pushing into the Eurasian plate.
As for D2: D2 has a climate closer to Northern US. I would think this would be a bit like a large valley or basin near D1's mountains, but interestingly enough the Dfb climate type doesn't exist near the US's mountains. It does exist near the Himalayas though. From this link (please don't laugh at it) it states that this climate type is wide-ranging in temperature and is mostly found inland. One way to make this sort of climate 'happen' is if the tectonic plates we mentioned for D1 pushed a) towards the top right of the image, or b) pushed up, and then a little to the right in one order or another. The reason I recommend a) or b) is because of the inland nature of D2 - we can make D2 'sheltered' from its north and eastern regions by a mountain range. Dfb regions experience a wide range of temperatures as well as some degree of humidity. This can be caused by a combination of a monsoon in a 'rainy season', warm air rising up the mountains and settling down the valley, cooling the area down in falls/winters and heating it up at other times.
Region A - we should have started with this: From this link, we can see that the Cfb region is forested and fertile. A nice thing about this region is that it has humid air flowing through it and this air is stopped from continuing further thanks to the mountains of D1. This area (like northern Europe) can also be low-lying. So I'd like to add to the tectonic plate history here by saying not only did T1 and T2 collide, but T1 also 'rose up' a little while pushing against T2. At the same time, sea levels receded. This would mean that although region A is forested now, it was at some point at least a shallow sea or a series of lakes millions of years in the past.
Region C: C is made up of cold hills/plateaus. So this complicates the tectonic plate thing slightly. So although the T2 and T1 definitely did collide, there was a bit of a rotation taking place, with region C acting as a 'pivot' around which T2 collided with T1 in a counter-clockwise manner. This is why region D1 has a mountain range, while C only has cold hills. The lower temperature of C than D2 is caused by cold mountain winds flowing down from D1.
Region B: So this region is very very fertile. In real life, a good chunk of China lives and eats from here, and this is where a large number of Brazil's population lives, as well as Uruguay, Paraguay, and most of Argentina. Cwa climates are noted by warm temperatures. Earlier I mentioned wind currents from the mountains freezing up region C. But where do these winds come from? I'm thinking that the air in this island flows from right to left: ocean winds from the right side of this map go up the mountains, cool down, and flow down the the cold steppes of C. But regions A and B don't have a mountain ranges blocking the path of the ocean, so instead the winds go straight through. But not exactly - thanks to region D2, some of the wind ends up 'settling' and circulating there, causing the sea winds I'm referring to to kind of travel from the right and split into 2 parts - one part providing warm air to region D2 and the rest flowing smoothly through region B. This 'fork' in the windstream carves out the land in region B, creating a large hill or mound, referred to by your Blue Star. This won't be a proper mountain, but kind of like a plateau of sorts. Also (if you like these ideas) this plateau would have to be bigger and located a little more to the north compared to where it is on your map now.
Finally, we have your Red Star freshwater caldera lake (crater lake as you called it earlier). Search up Lake Toba - it's a beautiful place is also an extinct supervolcano comparable to Yellowstone. Maybe this place is like that? Search up other supervolcanoes while you're into it. Supervolcanoes are made when a lot of magma gets piled up between the crust and mantle, and that's mostly what I understand about them. If you don't like the idea of a volcano, maybe you'd prefer asteroid impact, like this one. The link I shared refers to an impact on a coast, so if you want a more inland example, perhaps this lake would interest you.
I realize that my descriptions are a bit vague and hard to follow, so I decided to get on OneNote and do some drawings on your map.
Now a final note about the location of this island. Not too many places fit the region of the world where such conditions are possible, but you were right about picking the big oceans. I personally think that this island's southern half would fit really well in the Pacific Equatorial Current or its nearby countercurrents. More specifically, I would center the Pacific Equatorial Current on your island's lower half, allowing its upper half to not be as windy. So the region I suggest can be seen in yellow below:
Problem with this is that the Pacific Equatorial Current flows the exact opposite direction of what I described in my answer. There's a simple solution for this - your map is upside down! So, the upper part of your map is actually pointing towards Antarctica, or South Pole, in real life. That's why I have an upside down compass in the drawings I made on your map.
I hope this helps!!!
