At present on my 2017 iMac 1TB hard drive I have one container with 4 apfs volumes, for running High Sierra, Mojave, and Catalina (2 volumes for the last one). I’ve seen at least one article which indicated it would be better/safer to have the MacOS versions in separate containers. Any views on whether that matters?
I agree with the separate container recommendation. In fact, Apple has previously discouraged users from booting more than one macOS on a single drive, but that was before APFS, so not sure what their stance is now.
Apple had a support article that doesn’t discourage it.
It should be a separate APFS volumes in a single partition, sharing space. Obviously this means High Sierra or higher for the multiple installations.
I’d say that you’re fine the way you have it.