Catalina creates two partitions, one with the "name" that you know, and the other with "name - data"
It's still one drive, but two partitions. One (name) is read-only. The other (name - data) is read/write, and is the partition where all your files are kept. It might be confusing when you first see it, but you don't need to change anything about how you work with your files, etc. The system knows what to do with the two volumes, and the Finder will know where everything is.