Linux

There are some android based handhelds in the 200€ to 350€ range that can play a lot of emulated stuff as well as a solid number of PC indies/older titles through translation layers.

You can also grab a Retroid Pocket 5 and install Rocknix Linux on it if you want to avoid android, but it'll be more limited when it comes to playing PC games until the modding community figures out how to incorporate valve's arm translation layer.

I don't think something like that will ever exist. There is stuff like the R36S (https://r36sgameconsole.com/) that is great for older games up to the PS1. That thing also runs emulationstation and arkOS.

But PS3 emulation (and PS2 to some extent) is fairly taxing - so a 150 bucks device will most likely never be able to provide a good experience. I'm pretty sure that RPCS3 is expecting a RX5000 or a GTX 2000 series card which by itself costs more than 150 bucks, even now lol.

Yeah the retro gaming handheld community has some Linux viable ones with PortMaster but its just not the same as an officially supported mini Steam machine. I know its silly but I want one that is pocket-able instead of the massive SD.

That being said I love the Miyoo Mini Plus and other linux handhelds. They are flipping awesome!