Best way to multi-boot?

[Doc69]

What is the proper or best way to install multiple versions of MacOS on the same computer? Internal or external drive? Can you put different OS's in the same container, i.e. Mojave and Catalina on separate volumes in the same APFS Container, or is it best to keep each OS version in its own container, but 2x Mojave in one container is OK? I need a couple of installations each of Mojave, Catalina and Big Sur. I have tried most combinations already, having multiple installations on both the internal and an external SSD, and haven't really noticed any problems. But I do have some issues with my computer and thinking it may be at least partly related. It would be most convenient to have all installations on their own volume but in the same APFS Container, but I can imagine that this could cause some problems.

 

[joevt]

Separate partition / APFS container for each. Doesn't matter internal/external.
Each OS will have it's own Recovery volume, but maybe only the last installed OS has the Recovery partition working with Command-R key press? In that case, a boot loader like rEFInd can be used to boot the Recovery partition of a different macOS.

 

[Fishrrman]

You can create separate partitions/containers if you wish.

However... over years and years of keeping multiple OS's from which to boot (from back to the days of 10.3.9 -- actually, back to the days of the "classic" Mac OS), I've come to the conclusion that "the better way" is to have a "dedicated drive" for each boot OS. Things just work better that way...

 

[Joeronzk]

You can install multiple instances of macOS on the same drive after creating a partition for each. However, this is not recommended as it could be messed up if some of them broke up. I prefer to run additional macOS instances on portable SSD, which is more secure and managable.