I did a summarized writeup of what worked for me, I am running the full desktop 64bit but it should still work because the issue isn't that it's 64 bit: https://www.reddit.com/r/raspberry_pi/comments/spilo8/comment/j3w2962/?utm_source=share&utm_medium=web2x&context=3

I'll just quote it below:

"I'm running the Raspberry Pi OS Full 64bit Desktop version with Debian Bullseye (I referenced this guide from Ian which below is just how it went for me...)

I ran a casual sudo apt update && sudo apt full-upgrade

So as of 1/10/22 it was a fully updated, pretty vanilla install with just PiHole running and an install of Home Assistant in a Docker container which I hadn't really messed much with to be honest. I run the video output to my TV with HDMI from the mini port. Audio works.

Switched over to TTY2 with CTRL+ALT+F2

Logged in again in the TTY2 and ran sudo apt install steamlink and installed everything the package initially pulls in.

Still in the TT2, I ran steamlink to start it up because I know, just like regular Steam, it starts up and has to pull extra packages to do it's thing so let it install all those extra packages and it will ask you to press enter at a few places to continue on.

Eventually in the TT2 it will startup Steam all fancy like. I believe the interface is straight up from the Steam Deck because it's referenced a lot but it's not big deal. It's way better than the steamlink app was before which is great! It basically just used to be Steam Big Picture which was fine but not quite as sharp as this new hotness.

I have no idea when they might make the app run like normal but the steamlink app I believe runs it's own compositor which is the reason it can't run in X11 which makes sense. I think it has to do with Gamescope which is a great technology from what I've read into. However, since you don't need an X server to run the steamlink app now, it'll probably make it much simpler to make your own steamlink box from a Pi :)"

@N_mag this was super helpful in getting it setup and installed. Is there a way to make it auto run in tty2 that you're aware of, so it can just boot into Steamlink whenever I turn on the Pi?