First, there are two distinct "Recent files" in Gimp:
- Those in
File ➤ Open recent (Gimp edit history)
- Those in the
Recently used tab in the file selection dialog from File ➤ Open... which are shared between applications. For instance, a file freshly downloaded with Firefox will appear here in Gimp, and conversely you can export a file in Gimp, and then immediately upload it in Firefox, where it will appear at the top of the "Recent files".
This is all about the second ones.
The Recently used files in Gimp come from the file .local/share/recently-used.xbel. This file is normally shared among applications.
But in some packagings (flatpak, at least, IIRC) Gimp is "sandboxed" and made to see a virtual file system where directories can be different from those of the rest of the OS, and this makes it use its own copy of .local/share/recently-used.xbel that defeats its purpose.
I no longer use the Gimp flatpak, but at the time I managed to fix the problem by replacing the .local/share/in the flatpak by a soft link to the real .local/share/. You can't link recently-used.xbel directly because to update it applications (including Gimp) erase it and recreate it and this replaces the soft link by a real file. Linking the parent directory works because the applications do not remove/replace the directory so the link remains. As far as I could tell this has no ill effects (recently-used.xbel appears to be the only file that Gimp uses in it).
Another side-effect of sandboxing was that Gimp had its own private /tmp so you couldn't share files with other apps that uses /tmp for this (in my case, the Spectacle screen capture app). But this could have been fixed.
