Yeah, I have a Steam Deck, and it’s literally just a PC in the form factor of a Switch. It has a BIOS menu, you can install Windows on it (but you really shouldn’t), you can install a different flavor of Linux (I recommend Bazzite) – you can even install and play pirated Windows games through Proton, more or less fine, though you have to work for it a bit more.

They developed Proton so that they could get Windows games working on the Deck, and the reason they didn’t make the Deck run Windows is they wanted greater control over the OS than Windows affords. Proton has benefited all gamers on Linux. More recently, they’ve officially partnered with Arch as of a few days ago (which is what SteamOS is built on): https://www.tomshardware.com/software/linux/the-arch-linux-team-is-now-working-directly-with-valve-steamos-and-arch-should-both-benefit-greatly

and just to gush a bit more: the Deck is the only thing I can remember pre-ordering in the last 10 years and being genuinely happy that I did.