The topmost of the three "Macintosh HD - Data" - the one that says "Mount Point: /System/Volumes/Data" is the one that houses your user account, the one that is in use now - where your home folder, Documents, etc. are.
This, however, is pretty small: about 17GB. If you are not missing anything there (not a lot photos, videos, music?) and all your stuff is present, then that is fine. Let us know.
You can delete the last of the "Macintosh HD - Data" volumes - the one that says
"Mount Point: /Volumes/Macintosh HD - Data"
If you end up determining that the big one can be deleted, you will get a lot of space.
But be careful...
Try to mount that volume: select it and click the Mount button. Does it mount? Look for the content in the Finder, and see if there is stuff there that you want to keep.
To do that, select the volume, control-click it and choose Delete APFS Volume.
The big question now is that one volume that is unmounted. That is the one that uses the most space - some 200GB.
If you had a lot of data and it is missing now, that is where it probably is...