Questions about dual boot installation with APFS volumes/data

I am setting up a Mac Mini with 2 500Gb SSDs and want to be able to dual boot into High Sierra and Catalina and future macOSs.

I initially copied an another HS SSD that had been incrementaly upgraded from 2 OSs ago onto 1 SSD, and did a fresh install of Catalina on the 2nd SSD and transferred files from the first SSD via the Mac transfer. All worked fine but I realised that this isn’t optimal with 2 installations that will get out of sync with App updates etc.

So I was exploring the option of installing both OSs in their own Volumes on the same SSD that would share the same Data volume.

However, when I examine the Catalina SSD I see a Volume with the Catalina installation (~10Gb) and the rest of that SSD is a data volume. If I look at the High Sierra SSD, there is no Volume for the OS and just one Volume for everything - so OS and data are in 1 volume…

So, my question is, can HighSierra be installed in a separate Volume that will be able to share the same data Volume as another APFS macOS?

In theory yes, but in practice who knows, especially with the tougher security requirements in Catalina. If you go to your user in system preferences and select your user, you can then right click for advanced options. From there you can set the home directory, which can also be on a different drive. Your safer bet might be synching as much as possible via iCloud if possible.

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Thanks. I have abandoned this idea mainly because Catalina was so awfull. Switching between Catalina and any other macOS is just s stream of password, and extra verification stages.

I am sticking with Mojave for the foreseeable future. It feels like the sweet spot in terms of stability and still being able to use 32-bit apps. The choice is made a bit easier when your computer is not able to run Catalina though.

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