Considering all this work is open-source, could some third party make a Qualcomm Snapdragon based handheld console, if Valve decides not to make a Steam Deck Mini?
I really loved the idea of the Steam Deck, but I'd prefer to play something that's more like the size of a PSP or a Switch Lite at most.
GTA V is running at high preset locked 60fps via GameHub on the Ayn Thor which has a Snapdragon 8 Gen 2 https://www.youtube.com/watch?v=EMIPlwoAt58#t=14m41s
Some powerful retro handhelds support Linux loading, such as: Retroid Pocket 5, Mini, and Flip 2 on the five-year-old SD865, and more recently, Ayn Odin 2 (original, Mini, and Portal) on the three-year-old SD8 Gen 2 (which is one version lower than the SoC in Steam Frame (SD8 Gen 3)).
So if we get a native arm version of Steam and Proton ARM64EC, we will essentially already have mini Steam Deck(s), and since you want something similar to a PSP, you can check out the Ayn Odin 2 Mini, it's similar to the PS Vita, but I'm not sure if it's still available for sale, or you can order the Retroid Pocket 6 (available in a few months), which has the same chip, but a better screen and is also small in size.
https://wiki.postmarketos.org/wiki/Steam states that you can simply run the x86-64 Steam client under emulation, in FEX-Emu or Box64. Results on existing mobile hardware seem promising already.
There's already a ton of Snapdragon based handheld consoles, they're mainly marketed for retro system emulation but you can do whatever you want on them. They usually run Android out of the box though, not plain Linux.