Is this possible? Can I use the USB installer as an alternative boot disk to run MacOS on my MacBook Pro and then switch back later to boot off my hard drive with Mac OS Mojave? In other words, can the USB installer also be used to just run Big Sur on my Mac without messing up my primary configuration with Mojave? If I do this will I run into issues with icloud apps or will I need to use a different apple ID when I'm booting into a different drive running a different OS version?
I only need to use Big Sur with next years version of Turbo Tax. This is the last year Turbo will support my using Mojave. I don't want to upgrade my Macbook Pro to Big Sur on my main hard drive. I have some older 32 bit apps I want to keep using.