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:

docs.flatpak.org/en/latest/tip

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:
github.com/tchx84/Flatseal/blo.

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