Yes very much this. It is possible to modify an existing prefix but there are quite a few things to do, it's easier to back up savegames and game config files and then create it anew.
Thank you very much to both of you. Got it running flawlessly with CM on Steam Deck OLED at 90fps using GE-Proton10.34 and LSFG-VK for frame-gen. This one goes straight to the top (alongside DR2.0 and AC Rally) as favourite gaming on the go.