SmartGit 20.2.1 will allow to switch to an alternative SWT implementation which supports GTK <3.20. If you are running such a system, SmartGit will tell you on startup. Following steps will be necessary:

      1. If you have installed SmartGit < 20.2.1, install the latest bundle from the SmartGit download page.
      2. Locate smartgit.vmoptions: usually it’s located at ~/.config/smartgit/smartgit.vmoptions (if not present there, check the parent of SmartGit’s settings directory, as displayed in the About dialog). Add following line to this file: swtver=4932
      3. Restart SmartGit: if everything is configured correctly, SmartGit will print an information about a custom SWT version to terminal and should start up properly.