If you want to compare Manjaro with Arch you should switch to the unstable branch and update both systems at the same time and redo your tests. Switching Branches - Manjaro Outdated packages may create different results …
Also check ProtonDB for possible quirks needed to run games: https://www.protondb.com/app/2139460
Personally I’m working on the not yet released Manjaro Gaming Edition and had so far no crashes with games I tested it with. That OS will be launched with the Development | Q&A | Zotac Gaming ZONE and Development | Q&A | OrangePi Neo-01 most likely end of Q3-2025. Gaming is done via Gamescope similar to SteamOS.