Speaking of Steam Deck, is it worth the effort to invest in making one via Raspberry Pi?
I don't think you can still buy the original Steam hardware version in Canada where I live.
Almost certainly not, in terms of time-money tradeoffs as well as the final result probably being less of an integrated thing. There's been an onrush of Deck clones lately from all sorts of companies, and a lot of them look worthy of interest. See ETAPrime's Youtube for coverage.
Based on my experiences trying to get Windows stuff working through WINE/Lutris/Proton on my Arch Linux laptop/desktop, I'm guessing that a huge part of why they're able to make the SteamDeck a good experience is being able to guarantee that all the software they've written to help with compatibility is tested on their exact hardware. It took me a full weekend of tinkering to get ray tracing to work on both my desktop (which uses an AMD Radeon RX 6900 XT) and my laptop (with a mobile 3070); even after getting Lutris to use Proton Experimental that I downloaded through Steam, I still needed a smattering of different environmental variables (only some of which were the same for both AMD and nvidia) along with a newer version of mesa (for DXR 1.1) that's available even in the Arch, which have a reputation for bleeding edge stuff (although since then it's been put into their testing repos, so hopefully it will get pushed out soon). Even after finally getting the configuration so that the GPUs successfully reported the ability to do ray tracing, it took some specific configuration of the WINE prefix itself to be able to get certain games to allow the setting to even be enabled; apparently the Windows 10 prefix that WINE created had its registry initialized with inconsistent values for the OS patch build number it would report to software and the human-readable version of the string, both of which were old enough that the games didn't believe that ray tracing was actually supported, so I had to update them both to the corresponding values for a new enough Windows 10 patch before I could even enable the ray tracing settings.
Long story short, I have to imagine that even if someone managed to make custom hardware that was powerful enough to run the games they wanted, trying to just install the custom Linux distro that SteamOS uses would not just magically run arbitrary Windows games well. This really seems like something where the hardware and software have to be designed and tested in tandem to be able to have any level of confidence in a good user experience.
If you don't care about ray tracing, Linux gaming on Steam is pretty much install it and it works. I enabled the multilib repos in arch, installed steam from pacman and that was it. I was playing games immediately.
You don't need to mess around with lutris/wine, Steam just does it for you with proton. At most you can install proton ge[0] to see if it fixes some problems with proton for the game you're trying. But if the problem is with proton, you'd have the same issues on the steam deck as well.