Catalina shook up volume organization, but you can still make a restorable backup.

Until macOS 10.15 Catalina, Mac users knew: their startup volume was a single volume, just as it appeared! (Okay, for Fusion drive users, there are two physical drives managed by software to appear as a single “disk drive,” but that’s separate from the data organization that is a volume on a drive.)
…
Read full post here:
https://www.macworld.com/article/3513910/how-to-clone-a-macos-catalina-drive.html