Assassin's Creed 1 on Ryzen 5950X with Windows 11
Older games love to detect what hardware you have and try to figure out the best way to run. This breaks when the future comes along. Assassin's Creed 1 is the latest game I've had to tinker with to get running. You have to set the process affinity to use 2 or 4 cores. I set it to 4.
Create a shortcut to the AssassinsCreed_Dx10.exe file and alter the target to the following. Make sure it's pointing to your steam or games path for the game file:
C:\Windows\System32\cmd.exe /c start "" /Affinity 15 "S:\Steam\steamapps\common\Assassins Creed\AssassinsCreed_Dx10.exe"