I would like to know if there is a good open source project that let's me run a copy of a game on my phone without crashing or bugging out after a day or two, nothing on the app store works well enough. I just want to enjoy multiple accounts on an old 32bit mmorpg from 2013-2014.
Shelter, Insular (f-droid, FLOSS fork of Shelter), or Android Work Profiles/User Profiles if your phone lets you manually control them. If not, Shelter or Insular manage it for you.
On Samsung, Secure Folder will also do it.
These create a separate user profile that is shown with a little icon on the corner of the app icon, separate from your main phone user profile (this includes being separate from your VPN connection, if any, keep that in mind). They'll all do what you're trying to do if you stick your games in them.