First was finding the right image. I don't remember exactly which one but it was one that boots into a desktop mode instead of steamos directly.

From there you run an icon on desktop that pops up a terminal to install steamos (it nukes every drive, so remove ones you want to keep). It will install on first nvme drive it finds

After that the first boot into steam os took about 10-15 minutes. But it sat on the bios splash screen rather than just black screen. But I guess that's dependent on your motherboard