My 2014 MacBook Air just recently updated to macOS Catalina 10.15 today.
After the update I did a routine check on what's new & in the Disk Utility app something caught my eye for the volumes... there are now have two instead of the usual one. Usually I would only see "Macintosh HD", but now there's "Macintosh HD - data" as well:

Two Volumes

Why exactly do I have a "Macintosh HD" & a "Macintosh HD - Data" as volumes in Disk Utility?

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