Now I have replicated the error and meanwhile looked at GPU-Z. You can clearly see a spike in "GPU Clock" during the error. From otherwise 0.0MHz at idle/watching video, "GPU Clock" went to 429496729.0 at the time of the blackscreen?! Also "Memory Clock", UVD & VCE are clearly up (numbers are not in the screenshot). Can any of you figure this out? What is happening with my GPU?
GPU-Z (Spike while blackscreen/error):
Spec: GPU: RX Vega 64 (NOT overclocked). CPU: AMD Ryzen 5 2600X (NOT overclocked) RAM: 16GB Kingston HyperX 2933MHz BaseBoard: TUF B450-PLUS GAMING ASUSTeK Boot Disc: Samsung NVME SSD 970 Evo 250 GB OS: Windows 11 Pro 64-bit (problem also with Win10)