When I build a DMG on my macbook (Monterey, 12.3.1, xcode 13), the background image works.
If I build it on a GitLab runner (macos-12-xcode-14), the background image is not visible after opening the DMG.
The hidden .background folder is there and the background image is inside this hidden folder. It's not visible when the DMG is opened though. I saw some other issues posted here that mentioned issues with spaces in the title. Removing spaces made no difference.