Ubuntu comes with two versions of GIMP (as many other software for that matter. Snap will install 3.0.0 and apt uses 2.10.36. I thought 3.0.0 would be better, but it cannot open HEIF files, while apt's version can. I guess it it related to dependencies, but still. I'd like the bells and whistles of the 3.0.0 but alas, I am stuck with 2.10.36 for now.
Is there a way to open HEIF files in 3.0.0?
If the apt version does not meet your requirements, then I'd recommend the AppImage version (3.0.2 at this writing, "Current Stable Version" as of March 23).
My very personal opinion is that AppImages are to be preferred over anything Snap; as they generally are better behaved than Snap.
Gimp 3.0.0 supports HEIF.
Check that in the standard plugin directory (so, probably in the virtual FS of the Snap) there is a /usr/lib/x86_64-linux-gnu/gimp/3.0/plug-ins/file-heif/file-heif executable. Your system should of course also have the library /lib/x86_64-linux-gnu/libheif.so.1
In practice, Gimp3 is still pretty much in a state of flux and I would expect at least monthly updates for still quite some time, which is much faster than what you'll get from Canonical (if any...). So if you want an up-to-date ".deb" Gimp3 you can install from a PPA such as this one.
Edit: It's an issue with the snap. From the comments it already has a fix that should be rolled out in a few days.
I have the same issue with GIMP 3.0.
Looking in Edit->Preferences->Folders->Plugins lists two directories.
~/snap/gimp/502/.config/GIMP/3.0/plug-ins is empty
/snap/gimp/502/usr/lib/x86_64-linux-gnu/gimp/3.0/plug-ins has a lot of content including executables starting with file-* but no file-heif
The github for file-heif says it’s part of GIMP v2.10 so shouldn't need to be installed. Looks like an issue with the GIMP snap.
GIMP 3.0 issue and you should report it as a bug. I will when I get a moment.
I hope that helps
The issue is now fixed, cf https://github.com/snapcrafters/gimp/issues/390
Gimp 3 from snap can open HEIF files.