I had uninstalled the drivers (this time using the AMD Cleanup Utility) and installed the newest drivers afterwards by using the device manager instead of using the Adrenaline setup. Now the instant restarts are back directly once I start AC Odyssey. The random Hunt Showdown crashes are back too.
Now I lost my trail which leaves me completely frustrated. I guess I am going to send it back and try a new one. If that does not solve the problems, I will switch to nvidia and never go back to AMD graphics again.