Removing "Other volume in container"

I've seen two Data volumes, but so far, in all those the first Data volume had all the files and the second one had only a few MB and could therefore be deleted. I am hesitant to suggest you delete either because of the GBs they contain. So, the only way I would approach it is to first make sure you have a complete backup and then boot into recovery, delete your entire disk, and then install a brand new download of the OS. You can then transfer over your files - I am afraid that if you restore from your backup, you may wind up with the same mess.

Maybe someone will chime in with a better idea.

Okay, I'm not an expert with this, but first, the Mac HD - Data volume only shows 10.36 GB which is completely unrealistic. That volume is supposed to contain all of your apps, your files, photos, videos, whatever. The Mac HD volume is realistic showing 11+ GB - that is your OS and system. Then you've got what appears to be 3 volumes which are not mounted and are 85+ GB. I am assuming that one or more of those contains what should be on the Data volume.

And please highlight the third entry (greyed out) Mac HD volume and post what it says. That could be a duplicate of your Data colume (or not).

So, can you detail exact steps of what you did before you noticed theis?

We need some more precise information in order to help:

post a screenshot of Disk Utility window with all volumes/containers showing in left column.

I really meant the overview window showing the left column with all volumes/disks. The storage is neither accurate usually nor does it show the container(s), volume(s), etc.