Can I blow your mind for a minute?
There are bacteria that do photosynthesis from the infrared glow of hydrothermal vents at the bottom of the ocean.
Link here: https://www.pnas.org/content/102/26/9306">https://www.pnas.org/content/1...

This is 2.3 km down in the deep dark ocean. High pressure. No sunlight. Just hot glowy rock.
(I& #39;d known of this but just hit the article again during a literature search. Am still blown away by it.)

So. Imagine deep bottom of ocean on Jupiter& #39;s moon Europa, or even way deep in core of Enceladus. Same-ish pressure. No sunlight. But could have infrared glow from rock. These microbes could still do photosynthesis and get energy. And you have harvesters, you can have predators..

So you can have a whole photic-derived deep ecosystem that DOES NOT requires chemical disequilibrium. Just normal geophysical processes. (Yah, OK, you gotta have building blocks. But now we know that CO2, CO, H2, NH3 are good enough.)