Is anyone doing multiple macOS on this build? I want to be able to boot Big Sur, which is working fine right now using OC 0.7.0, and also boot Windows 10 Pro, also working fine, and now also Mojave (for 32-bit apps I still own that are never going to be upgraded).
I installed a second 250GB SSD (PNY) and then built a Mojave installer USB using the create media method. Did nothing else. Booted OC, selected the USB installer, and installed Mojave to the new SSD. Now, I can boot OC and select Mojave disk - it boots, but of course I see the "complaint" about Incompatible disk features because APFS is different on Mojave and Big Sur. I ignore that and I've tried my apps which are installed on an external 3.0 drive. Works great. I'm just curious if I am missing something? Can I proceed to install Catalina in a similar way? I have not tried to set up Apple ID, etc. on the newly installed Mojave.