I made few changes in the way the fontconfig libraries are detected and handled, such that the AppImage should work fine on both old and new systems.
RawTherapee-dev-5.4-266-ga84ce624.AppImage should now work OK on both your laptop and desktop. I will update the other packages once I have confirmation for this one.
I am now trying to figure out the reason for the sluggish performance of the UI that you and @Morgan_Hardwood reported, and that I can also reproduce. It seems to be related to SVG icons being loaded instead of PNG ones, but I am still investigating…