ThomasHelzleI solved this a while ago with the help of support and thought I mention the solution here:
Same problem here. RM 21.3 works fine with the Qt4 version of Houdini 16 but not with the normal Qt5 one.
But for me commenting out Renderman does not solve the problem. I first thought it did but I accidentally started the wrong Houdini version, using Qt4.
So must be some other Qt on my system, although my path etc. seems clean…
I had QT dlls in my system32 folder which seems to override every other installed version. I don't know what software installed them but deleted them anyway and from then on Houdini with QT 5 worked without problems.