Asus and Lenovo both make a handheld gaming device that competes with the Steamdeck now. Though the Orange Pi Neo looks like an interesting entrant. Manjaro is pretty similar to the Steamdeck OS, which Valve has failed to release for other hardware (they said they were going to). In fact, Manjaro is what Valve recommends to developers looking to test their games ona "steamdeck like" OS if they don't have a Steamdeck.

you'd actually be surprised how much competition there seems to be in the chinese SBC gaming space

it's mostly emulation, though (see https://www.reddit.com/r/SBCGaming/)

For playing Windows games, mostly.