Afaik, this should be it:
Iirc, if your ROMs match the names expected by the database Retroarch checks, it should load the box arts automatically.
The older Bomberman games, the Metal Slug games from the Neo Geo, Gunbird, King of Fighters 2002, Final Fantasy games like II (PSP is the most complete version), VI and Mystic Quest, コテ・DE・メクール (a PC-98 game), the first Shantae, modern homebrews like Tanglewood, Nyx - The Paradox Relic, Augury Red Code and Micro Mages, Mega Race, Kunio-Tachi no Banka (rebranded as River City Girls 0 in its recent release, and has an option to play with untouched dialogues), Wonder Boy in Monster World, Castlevania: Symphony of the Night, Phoenotopia (Adobe Flash version).
There are cases where AppImages aren't viable indeed, like with programs that require ring 0 access. But limitations exist for all formats, so perhaps another good alternative is having multiple versions of a given program, like downloading the equivalent deb package through apt while also keeping the appimage version. It would bloat the storage for a potential automated configuration, but it should help with ensuring compatibility.
One thing I like to have with me is the AppImage version of programs when possible, since they usually work out of the box. Also helps ensuring I don't depend on the availability of whatever package manager the system uses.
If size is of matter, I would imagine it's due to being small, but with great potential for growth and diffusion, instead.
But like you said, and perhaps in a lighter point of view, it may indeed just be that same diffusion picking communities with established cultures already, instead of potential bots and paid actors.
I saw a post earlier today suggesting quite a lot of those political posts may be coming from bots or paid actors. And considering those post more often than not also carry stigmatization and faith-like views, even if it's made by actual users, I think it's still a good call to at least keep a lower tolerance, maybe avoiding the rage-click posts and communities and sticking to more informative posts instead.
Also dunno why the voting ratio.
And since around Reddit (back when I used it) and the federated platforms, seldom I see complaints about the store, the next best possibility I can think of is that maybe people don't like being suggested stores/platforms other than what they're used to, like how I'd often see when commenting about GOG and Linux to Steam and Windows users, respectively.
Bravely Second and Rat King Adventures. To me, the former is being pretty fun, even more than Bravely Default, at least some 8 hours in, with the only potential problem being levelling feels way too easy. Rat King Adventure is also nice, although I'm not a big fan of roguelikes, and it got me curious since it's rare to find FOSS games.
Not familiar with that operating system. Sorry. =/