Thank you all for offering your help. After a couple of days of intensive testing I know for sure now that the reason for my sims hiccups are problems with the speed the sim can draw data from the internet.
The weird thing is, that the sim only stutters in VR mode when the internet connection is slow.
Yesterday MSFS performed completely stutter free. That proves that my pc is fine, including my headset, gpu and cpu.
Since others were also seeing stuttering and low bandwidth issues it might have been the servers, but I don’t know exactly.
Anyway this sim depends greatly on a powerful pc and a fast internet connection. If one is missing, there’s no fun.