I recently added a volume, via disk utility, to my MBPro 2017 for a separate volume to install Big Sur.
Opting to maintain other installations of High Sierra, and Mojave for the time being.
I notice that Big Sur installed 5 separate volumes
• Two volumes each labelled Volume: APFS System Volume • APFS/macOS 11.1 (20C69)
• One labelled Volume: APFS System Volume • APFS/macOS 11.6 (20G165)/System Snapshot Mounted (center pane)
• One labelled APFS System Snapshot • APFS/macOS 11.6 (20G165)/ com dot apple dot os.update…(snapshot name line item)
• and lastly
Volume - Data/APFS/macOS 11.6 (20G165)
Of the two Big Sur 11.1 volumes, they each have differing incept dates, but each contain virtually the same (duplicate) 15GB content of Applications, Library, System files
This is beyond my ken
Don’t understand the newish APFS scheme of things, and don’t understand all the reduncancy
They’re not duplicates, They’re hard linked. If they look like duplicates to you, that’s because that’s the way the split was designed to work. One is the read-only core macOS, the other is the user-writable data. The hard links are what makes it all come together seamlessly.
It’s really a quite smart layout despite us not being used to boot file systems being organized this way. Here’s some recommended reading.
The first advice is do not try to understand completely. Read Howard Oakley’s articles (https://eclecticlight.co) for educational entertainment and note his opinion of missing documentation.
Second, consider the possible conflicts between multiboot OSes in the current macOS environment. Howard has documented many. If you really need to run the latest and greatest macOS* and also need an older version, I recommend you find an older model Mac mini and use screen sharing whilst allowing Apple to forge ahead with changes in file structures.
* Of course you do, if only to keep up with security updates and emoji updates.