Does it support "sending a file larger than 2 gigs, without mysteriously deleting it at the end, but if you manage to sneak a hardlink to the file while it's transferring then it's okay"?
A lot of times I start out with Normal difficulty, and a game eventually escalates its difficulty past what I am capable of delivering. At which point I find that the only way to change the difficulty is to start over, so I uninstall it.
If you set up flatpak as --user, bringing your home directory over would be 99% of the job.