I have a planet that is mostly inhabited by "animals" that aren't carbon based, with intentions for humanity to eke out a way of living there. Now, easily I could reason that they just HAPPEN to contain proteins and hydrocarbons but I want to see if I can make it even more realistic. Currently, humans and a few parasites they brought with them are the only terrestrial life on this planet. Not even rats came with them (Though a couple of stowaways from other planets did, this is several million years after the modern era.) With that parenthetical in mind, these also aren't homo sapiens I'm talking about, just a human lineage that has also evolved more robust metabolic systems. Without easy access to proteins and hydrocarbons, how can humans survive? Do organic compounds show up in inorganic sources (minerals, synthetics, etc)? Are there alternatives humanity might be able to consume that aren't exactly like those on Earth?
These humans are at a technology level analogous to colonial europe, with SOME scifi thermodynamics in play. I don't think they can simply manufacture their own food this way, and there are narrative reasons they haven't simply turned their parasites into protein livestock (they still think food poisoning comes from "bad vapors." The modern period will change this.) Additionally, life on this planet has evolved to look and act as unlike carbon-based life as possible for narrative purposes (we can say it's to avoid predation.) They need only look and act inorganic, though have incorporated more inorganic compounds into their biochemistry to complete the picture and likely consume more inorganic compounds than not. This leaves room for their own synthetic sugars/RNA to highly resemble carbohydrates and protein without actually being either.
90% of life on this planet is inedible, naturally. Human food sources are intent to come from the few places they can actually get that food. The period of discovery started when humans WERE capable of replicating their own natural food source, while scientific advances allowed for the discovery of local foods. I want to know what those could be like on a chemical level. I've exhausted google searches on "inorganic foods" ad nauseam.
Edits: As per other comments, conditions on this planet are similar to early Earth in terms of geochemistry. There's still oxygen and plenty of oxygen replicating lifeforms. The point of this experiment is to answer "How would humans survive (and answer why they survive) if they, without assistance from technology, were plopped on a superficially habitable alien world."