Really? I use Arch native Steam and Proton no problem. You either use steam-runtime (uses built in Ubuntu runtime) or steam-native (expects Arch packages) but there is a meta package for pulling the runtime deps. Both have worked for me.
That said, Flatpak has come in clutch for me as well on the Steam Deck, and for things like Prism Launcher (modded Minecraft launcher) where you want to juggle multiple Java versions without needing to run archlinux-java between switching packs.