Mintbackup doesn't save app installed as flatpak

[Angedestenebres]

Hello;

Following a discussion about this issue posted on mintinstall: linuxmint/mintinstall#402 and after a discussion with the autor, we think the solution is there.

However, after trying mintbackup I noticed that flatpak apps aren't listed in the backup file.
Even if Mint doesn't provide any app with the default installation, flatpak and flathub are part of the softwares available on the software center and no doubt that a lot of users have them.

Could you please check how to hide that in order to provide a tool that save all installed apps?

Thank you.