PC randomly restarts after GPU upgrade

Hey people, wondering if anyone could help me out with a PC-problem. Recenlty I upgraded my GPU from a GTX 1080 TI to a used RX 6950 XT. With it I got a new 850 W PSU from Corsair and later a 1200W Straight Power 12 PSU from be quiet!.

After deinstalling Nvidia drivers with DDU and installing AMD drivers my PC would restart randomly when playing certain games. After a while (usually less than 30 minutes) of playing f.E. Red Dead Redemption 2 my PC would shut off (black screen) and automatically restart. No blue screens or any error messages to give me some indication as to what is wrong.

Any idea what steps I can take to identify the cause and solve the issue?

System Specs:

OS: Windows 11 Home CPU: AMD Ryzen 7 7800 X3D GPU: Asus TUF RX 6950 XT Motherboard: MSI MAG B650 Tomahawk RAM: Corsair DDR5 Vengeance 2x 16 GB 6000 OS Drive: SATA SSD PSU: bequiet! Straight Power 12 1200 W