Question: Can I install both High Sierra and Catalina on a single (internal) HDD with 2 partitions? I'm confused about the APFS thing, because when I installed the High Sierra, it did not change the drive to APFS and remained HFS+. So does that mean that Catalina cannot co-exist with High Sierra on a separate partition on the same physical drive?
And if that is the case, which OS should best reside as an external drive? TIA