If you installed GIMP from outside the repos at any time before the upgrade, it would make sense that it would be removed for compatibility reasons. Also, any and all installations from outside the official repos are not supported.
The reason GIMP 2.10 was not included in 18.04 is due to the fact that GIMP 2.10 breaks MyPaint 1.2 due to a library compatibility issue. Since MyPaint 1.2 and GIMP 2.8 are included in the Ubuntu Studio flavor, it would have broken the entire flavor. Additionally, GIMP 2.10 was released after the feature freeze. So, until MyPaint releases a 1.3 version, 18.04 will be stuck with GIMP 2.8. Ubuntu 18.10 will contain GIMP 2.10, and as such MyPaint was dropped from Ubuntu Studio until the bug is corrected. See https://bugs.launchpad.net/ubuntu/+source/gimp/+bug/1759625. Since this bug and workaround involves installation from outside the official Ubuntu repos, this bug is invalid. ** Changed in: gimp (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Studio Bugs, which is subscribed to gimp in Ubuntu. Matching subscriptions: Ubuntu Studio Bugs https://bugs.launchpad.net/bugs/1788943 Title: after upgrade to xubuntu 18.04 from 16.04, gimp fails to launch... Status in gimp package in Ubuntu: Invalid Bug description: I updated to xubuntu 18.04 a few days ago. First re-use of gimp (right click on image and gimp is missing from the context menu) leads me to discover gimp is no longer installed. `which gimp` as user and as root does not find an executable going to https://gimp.org shows me there is a new version, and incidentally a new install method. The method works. On the the gimp website, however, there is this perfect description of the current situation with ubuntu, and a clear request to take action. So, ubuntu, crew, please do the right thing. I quote (emphasis added): Once installed, it [gimp] will be made available exactly the same way as other applications (menus, desktop overview, or any specific application launch process used by your desktop). *If this is not the case, we suggest to report a bug to your desktop or distribution asking for proper support of flatpak*. In the meantime, you can still run it by command line (not as the recommended method, only a workaround): flatpak run org.gimp.GIMP//stable End of quote So, the workaround to the bug is included. Very handy. I would much prefer to be using the 2.10 release, with a proper install / distribution method, than the 2.8 release (and all the ppa nonsense put out on the web). ProblemType: Bug DistroRelease: Ubuntu 18.04 Package: gimp (not installed) ProcVersionSignature: Ubuntu 4.15.0-32.35-generic 4.15.18 Uname: Linux 4.15.0-32-generic x86_64 ApportVersion: 2.20.9-0ubuntu7.2 Architecture: amd64 CurrentDesktop: XFCE Date: Fri Aug 24 13:56:25 2018 InstallationDate: Installed on 2016-07-17 (768 days ago) InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1) SourcePackage: gimp UpgradeStatus: Upgraded to bionic on 2018-08-22 (2 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gimp/+bug/1788943/+subscriptions -- Mailing list: https://launchpad.net/~ubuntustudio-bugs Post to : ubuntustudio-bugs@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntustudio-bugs More help : https://help.launchpad.net/ListHelp