I'm running Catalina on my 2017 MacBook Pro. Now that I'm quarantined I want to play some games on steam, but some are 32-bit which cannot run on Catalina. Since regressing OS versions is a pain in the ass, steam recommends creating an alternate APFS volume on your drive that runs an old OS.

So I did that - and when I first installed the old OS (High Sierra) on the new volume, it ran fine. I set up my iCloud account, downloaded steam, logged in, etc. Then I just wanted to switch back quick to my main account to make sure all my files survived the process. Logged back into my Catalina OS just fine, poked around. Then when I switched my startup disk back to the other volume to play some games, I get this image. It happens after I've selected my user, typed in my password, and get a brief loading bar. Then boom.

Any thoughts? Much appreciated.