That's not my experience at all. The majority of games, especially on Steam, work out of the box.

I would advise the opposite: Don't get an old box. Take your new box, take a new hard disk, and just install Bazzite (and pretend you don't know anything about Linux, just stick with the defaults).

That didn't work for me. I had my email, documents, some software I used on Windows and files it created (think Photoshop and PSDs). I needed time to find out if I could find similar/equivalent software on Linux, set up new workflows for my work and stuff like that. So I had my primary machine still on Windows and used the secondary to see how all this would work. And then gradually moved all the software, data, and workflows to Linux, until I didn't have anything left that could only work on Windows (well, except games I guess).

As for games, I think a lot of them DO work on Linux but it's easier for me to have dedicates gaming rig on Windows instead of guessing if this new game that I like will work on Linux.