The two volumes are present "Mac SSD" and "Mac SSD - Data". However, the "Mac SSD" volume is NOT mounted, but instead, an "APFS System Snapshot" within the Mac SSD volume is mounted and seems to be where macOS is running from.
Yesterday I had ... 2018 15" Macbook Pro w/32 GB RAM + 2TB SSD running macOS 10.15.7.
There has been a growing list of oddities, so want a fresh start NOT restoring from my TimeMachine backup.
I created a new APFS Volume and called it "Mac SSD"
I installed Big Sur 11.2
Started to install all my software and data
Booted back to Catalina and noticed odd drives on my desktop
Checked Disk Utility, booted back to Big Sur, Checked Disk Utility
And here I am ... very confused.
It turns out that the snapshot is an intended security feature of macOS 11 and higher.