https://osgameclones.com/ is the best aggregate for this kind of thing.
https://libregamewiki.org/ also looks like something relevant.

Maybe now that we have a messy thread of various links, we can go check whether some of them are not yet listed in osgameclones.

YUNOHost iso is basically just Debian, but the one-click-install for various self-hosted things is it’s primary purpose. All done through web interface.

cool idea

concept somewhat reminds me of OpenDesk
https://en.wikipedia.org/wiki/Opendesk
Which I know about because it uses the same name as https://opendesk.eu/en/ , which I am actually interested in.
https://gitlab.opencode.de/bmi/opendesk/gitlab-profile/-/blob/main/README_EN.md

Pokemon MMO?
sounds like people should go play https://pokemmo.com/ before it gets C&D’d.

Other comments already pointed to some very good software solutions.
But I would argue that absolutely the biggest barrier to entry for the masses is hardware.
Restoring an old PC or making some cable spaghetti with some SBC is currently too advanced for average person.
Self-hosting for the masses would require some new form of home servers.
Something modular, where adding new components would be as easy as playing with Lego bricks.