I tried out the MegaGlest Flatpak
Worked well, but a couple things worth noting:
1. It doesn't use an existing $HOME/.megaglest folder for user data. The path is $HOME/.var/app/org.megaglest.MegaGlest/.megaglest
2. It doesn't come with 7z and there's a warning when I enter the mod center that files can't be downloaded or installed.
3. MG doesn't see a mod if it's being pointed to with a symlink (only tried with .megaglest/techs