Ouch, but not wrong lol.
Good recommendation, but I found something that I consider even better: Dual boot Mojave/Catalina from one APFS disk! I was a chicken and used a bootable USB stick that I put Mojave on, rather than going straight in with the native Recovery Mode. I now have a second boot option when I restart my computer, and have successfully run Avernum.
Sadly, it seems that Spiderweb pulled the Mac version of the Geneforge Saga off of Steam, so I can't reinstall it. Grrr....