No no…You misread everything ok, if you gonna do Steam i’ll list things you need now
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Make sure you’ve installed / have all requirements
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Re-read Steam section for everything you need to know, but tl;dr you’ll need:
sudo pacman -S steamand then launch Steam from your launcher, get account, buy game and follow 3. Steam 3.1 Setup to know how to enable Proton in Steam client UI and get you started
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That should be it, play

P.S. Stop aur everything it won’t make things stable 
P.P.S. I think you still would need to know what’s wrong with your pacman, probably you have multilib disabled or something like that