Also, why doesnt synaptic allow me or give me the option to upgrade this old GIMP version? I'd rather do that, because i probably could keep my settings/configurations & i wouldnt have to re-pin the icon to my taskbar.
Because the onus is on the Gnome GIMP developers to upload later or newer versions of Gimp. I realize that they will deny this, and that their denials mean absolutely nothing.
No, it is not up to the Distros to maintain the GIMP packages, nor do they change the GIMP dependencies.
Gimp 2.10.18 is the latest version that GIMP has uploaded to the Focal Repository.
If you want to keep the Flatpak version and remove the APT version,
sudo apt remove --purge gimp
Or, you can use Gnome Software to isolate it (Source button: Zorin) or use Synaptic (Version 2.10) to remove it.
Package updates are the onus of the package maintainer. As I understand it, in spite of Focal Fossa being LTS, the Gnome GIMP developers stopped providing updates for GIMP on Focal.
Bear in mind that Flatpak is a Gnome Project and so is GIMP. They are supplying directed pressure to favor their own teams interests, not the users.
Because of this, you cannot upgrade GIMP higher than the current version unless the GIMP developers yield and do the right thing for a change.
You can, of course, use the Flatpak version instead of the APT version. That may fulfill your needs for a higher package version. It is supposed to receive upgrades.