Comment by seba_dos1

Not sure what you're talking about, Flatpak runtimes are easy to find and contribute to: https://docs.flatpak.org/en/latest/available-runtimes.html

I wasn't directly involved, but the company I worked for has created its own set of runtimes too and I haven't heard any excessive complaints on internal chats, so I don't think it's as arcane as you make it sound either.