What? You have read my question thoroughly, understood it, and given a practical answer. In fact three answers. I’m not sure that is permitted on computer help forums
- Have you tried
flatpak remove --unused ?
An immediate fix. It has removed a Gnome platform which I had been using to develop an application, but which I’m not working on at the moment. It has saved about 1GB, which saves the situation for the moment. [Edit] I think this implies that removed paks don’t leave any junk behind, except perhaps platforms (and configuration files in ~).
flatpak --user install <app-name>
I remember when I used to use Snaps that they were installed in a visible directory in my home directory - which I really didn’t like. However this is at least hidden, although it means my backups must be arranged to exclude it. It will solve the situation for the short term.
- a custom installation with a different path
I think this allows me to put the paks anywhere I like, including a separate disk. No real advantage for me in this.
I have done 1 and will do 2 soon. ASAP I will install Fedora-35Beta on a new disk and double the size of my system partition at the same time. That way system and data will be completely separate and I can just backup the whole of the data disk.
Thanks for your expert help @felipeborges!