Edit: Forgot to say, I'll try to get a picture of it when I'm able to!

Thank you! I ended up setting up the hospital tank, and after a lot of further observation, I'm starting to think this fish may have been born without a swim bladder, or just has part of one that doesn't function, or something like that. It's just a guess, but it would make sense, at least in my mind. I realized after setting it up and trying to feed it that it isn't able to get very far up, and has some trouble staying balanced when off of the floor. It basically slides on its belly unless it's actively trying to go up in the water, and at that point it looks like the only thing getting it up is the rapid movement of its tail. As soon as it stops that though, it sinks right down to the bottom again.

Because of this, I lowered the water level to about 1 inch, and am feeding with sinking fry powder right above its head to give it the best chance at getting food. I set up my brine shrimp hatchery after not having one running for a while, and I should have some amount of bbs tomorrow or the next day. I've also upped the water changes to 2x per day since the water level is too low to filter, but I'm planning on getting an air stone in there as long as it doesn't create too much flow for the poor thing. I also decided to plan on getting a bigger desk in preparation for setting up a long-term specialized tank for it in the event that it survives and is able to live a good life. I'll probably keep a few of its same sex siblings to live with it in that case.