The steam deck uses KDE Plasma 5 as its desktop environment, so anything that uses that should feel very similar. I recommend bazzite if familiarity is something that would appeal to you.
It’s not about being able to push both movement buttons at the same time, it’s about being able to push more buttons in general. For hero shooters, mobas, MMOs, and other games with lots of inputs spreading out your reachable keys is really good.
Yeah I can’t say I’ve used it myself but it seems pretty straightforward and very in line with SteamOS philosophies.