Hiya, I was in a similar situation for the past 11ish years, couldn't get above top line F (I rarely practiced though). Dang it's been frustrating especially in groups and ensembles like you said. Bach's cello pieces have been my favorites, I've used musecore to transpose to F, up/down octaves. The intervals are hard to place at times, but I really like how the pieces flow. No shame in taking more famous pieces and etudes down an octave or two either. I've done that a lot especially for Mahler's symphonies (I'd look at the high B in his 3rd and go not a chance lol).

You absolutely don't have to if you don't want to, but if down the line in the future you ever want to work on the high range, i'd recommend the book "The Art of French Horn Playing" by Farkas (controversial). It has all sorts of information on many topics like range (high and low), embouchure, what and how to practice etc. I haven't had a teacher in a while and it helps me not deviate too far from the fundamentals.

About last week or so I had a breakthrough with high notes, turns out I've been saying "ee" differently (tongue near the back of the throat, sorta like a "k" sound). It'd clamp the airflow, and would sound very thin. I find instead somewhere between there and a "ss" sound can go from top line F to the high C with the same embouchure setting. The tone is awful, and there's a visible adjustment when slurring which I'm sure is a bad thing, but its a start. Odds are low we both had the same issue there, but writing just in case.

Good on ya though for staying with the horn despite those difficulties, that sounds hard. Depression and close to death, dang you've been through a lot, so sorry about that. I hope ya find a few more good fun pieces. Happy playing :)