The app run fine but ui are mass up and unusable because of missing themes engines, and it crash (I got segmentation fault) if I try to change theme to system theme it's fine 3 days ago
Gimp is likely still using gtk2, which means you need a theme that supports gtk2. That's probably old and un-maintained, since gtk2 has been End-Of-Life for a while now. gimp 3.0 is approaching though.
Is gtk not backward compatible with older version?
New main versions of software usually is not compatible with old versions. That's one of the points of new main versions. You cannot load Qt 3 themes into Qt 6 either.