sorry I can't be more help, I am in the middle of testing out an OpenCore Catalina setup.. Sounds like Apple is buggering it up in their effort to push people forward. I can tell you also that on Catalina, when I attempted to install GarageBand, it said something about needing BigSur, but then downloaded the highest version available for my hardware... of course after that, it started giving me annoying notifications that I need to update GarageBand, even though Catalina won't allow it. And I can't get rid of a notification to update to BigSur either...and my understanding is that Apple has gone out of their way to prevent anyone from being able to turn that off.
So basically as usual...they are burning the trail behind while they forge ahead.. I think in some cases they don't mean to burn the trail behind but they're so focused on ahead that the trail burns behind them anyway.
OSX 10.15 (Catalina) on OpenCore - Logic Pro 10.6.1, VePro7, Mainstage3
5,1 MacPro 3.46ghz x 12 96gb ram