Comment 2 for bug 1909807

I've merged my changes into the GTK3 branch (https://github.com/PintaProject/Pinta/commit/cbe442238ff1cc2fff5a4785ecc7861ffb00b488).
If you're able to do some testing with a snap / flatpak package, that would be great!

The only issue I've noticed so far is that https://gitlab.gnome.org/GNOME/gtk/-/issues/1820 prevents us from detecting the selected file filter and auto-filling the extension when FileChooserNative ends up using the standard GTK dialog on Linux (not sure if this also affects the portal case). This was fixed in GTK 3.24.21, but the Ubuntu LTS is still on 3.24.18 (https://packages.ubuntu.com/focal/libgtk-3-0).
I'm going to leave this issue open so that we can check the status of this before the release of our GTK3 branch and decide if a workaround is needed.