To me, all versions of krita available at that link require Qt5 5.12. But, downloaded the stable krita 5.0.6 AppImage from krita.org and all is well. And, 5.0.6 also uses QT5 5.12, but it is inside the AppImage. Might be worth checking out, whether it is that way with the nightly versions, too.
BTW and if really nobody found out yet, you can right click AppImages and Uextract them, and have a Rox-App. Well, works with a lot of AppImages, but not with krita unfortunately. For krita to run as a Rox-App, you need to write your own AppRun which exports PATH. (I used the AppRun from inside MyPaint AppImage and only edited the line where it executes MyPaint to krita, and then it worked)