Could I just make my own Steam Machine?

I'm currently playing games on my PS5 and my ROG Ally X handheld device that I run SteamOS on. I was interested in the Steam Machine because I wanted a console like experience but also be able to mod and use the system as a PC.

The Steam Machine looks great for my needs, though it's not powerful enough so my question is... Could I just buy a pre built Costco PC or even build my own PC and install Steam OS onto it, basically just creating my own Steam Machine?