gimp 2.10.22 supports AVIF. It is available in Ubuntu 21.04. Ubuntu 21.04 is not a long term support release, so you'll need to upgrade to 21.10 later this year and then to 22.04 LTS next year to get back to a Long Term Support release.
Or you can try installing the snap release of gimp. https://snapcraft.io/gimp ** Changed in: gimp (Ubuntu) Status: New => Fix Released -- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to gimp in Ubuntu. https://bugs.launchpad.net/bugs/1917514 Title: Add support for AVIF images To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gimp/+bug/1917514/+subscriptions -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
