It does yes. Although it launches Steam directly as its own .. "shelll"? Is that the right word? KDE is bypassed entirely unless you launch "Desktop Mode"

Anyways, I still wouldn't recommend Arch to a new user, go with something easier and more mainstream for your first Linux experience. PopOS, Mint, Fedora, Norabora, Ubuntu/Kubuntu

Also, saying Steam Deck uses Arch isn't wrong, but it's a bit misleading. It uses an Arch base , curated, configured and tested by Valve, and finally periodically shipped as updates using immutable root images (on a single well defined hardware platform). If you install vanilla Arch yourself you're responsible for all configuration and testing yourself.