Thanks for your tips and detailed Ideas.
I updated all the drivers, bios, AMD energy preset etc. right at the beginning and used the driver verifier, but that didn´t fix the problem.
All those classics as memtest, prime etc. didn´t show any errors, but I will try to test ram by ram chip in single steps.
The hint with the GPU, if it fits well, could be an option because this is something I haven´t tried.
It is crazy, that the BSOD are always different. "unexpected kernel mode trap", "IRQL_not_less_or_equal","memory management" etc.
Sometimes I think it is a ticking time bomb under the hood. I think it might be the ram, because there had been reportings of new but damaged G.Skill chips I am just wondering, that memtest didn´t complain anything at all.
I had some "seldom" moments the PSU made some crackling noise (not always when it is under heavy usage and 100%CPU workload) is this normal, my other PC had been very silent and the new system, (CPU fan as well) is quite noisy.
But I know it is by far too general for a remote diagnosis, so I apologize for my long post because I think I need to ask the reseller to recheck the whole system. There are too many sources for errors.
But thanks for your kind posts!