These AppImages are built and provided by the creator of Modding-OpenMW.com and are not endorsed or supported by the OpenMW team.
Verify files with minisign:
minisign -Vm <file> -P RWRhRQIxQyKu4Bpxy2AF5lB2el21dlVzMSPuTr3ThgYD3WskT80vbmTHAppImages are mostly useful for being standalone executables that just work. There may be an existing, official way to get a release build (e.g. Flatpak) but generally speaking you have to build it yourself if you want to try a dev build on Linux.
I make and provide these AppImages as a way for folks to get easy access to dev builds on virtually any modern Linux setup, and also for those that just a single, standalone executable.
Report problems specific to the AppImage here, source is located here