Some words of wisdom if you want to move your flatpak stuff from ~/.var to some other location, like another harddisc due to space issues:
https://docs.flatpak.org/en/latest/tips-and-tricks.html#adding-a-custom-installation
Due to that containerization and bwrap stuff you can't just move .var to another location and symlink it... like I tried, the lazy way.
You have to create a flatpak config and install/run stuff with --installation=extra.
Also make sure the mountpoint does not have "users" in the fstab, which in my case made the mount nosuid, flatpak/bwrap does not like that.
For Flatseal to work with custom installations, there are some extra steps involved:
https://github.com/tchx84/Flatseal/blob/master/DOCUMENTATION.md#enable-custom-installations.
