Autotrophs are lifeforms that consume simpler molecules than the large protein, carbohydrate and lipid molecules that heterotrophs like humans ingest, these large molecules are made by autotrophs and other heterotrophs.
On earth chemoautotrophs are tiny bacteria, living as a whole off fairly pure chemicals that are toxic to humans like sulphur and metals, but they needn't be. Perhaps chemoautotrophs may even given different environmental and evolutionary swings on earth have ended up being multicellular and of a similar size and intelligence to humanity.
Q: What food/sustenance could humans and chemoautotrophic lifeforms share in common in non tiny amounts?
For example Salt is nicely non human-centric while still being edible and helpful for humans, you can't really eat a big lump of salt in one go or live off it, but reasonably large crystals of salt can be used as an ingredient, compensating for dehydration by having the food be very liquid like soup.
Could, perhaps with work from both sides adapting, subtleties even be bought to similarities of pallet, keeping in mind that we vary so much among earth cultures and mindsets.
It's also worth considering the difference between politely trying something that won't be too harmful and consumption that sustains a being.