Why does Disk Utility show "Macintosh HD" on both Logical Volume Group and the volume underneath?
Why Disk Utility does it this way is a good question, but when both the drive and volume show like this, its a CoreStorage volume.

These terminal commands should put it back to the old way if it isn't encrypted:

diskutil cs list - find the "Logical Volume" (not Group) and copy the long "number" at the end of the line (it looks like this: BE1E16CA-64E2-494B-8EDC-3E843EF5C9A9)

diskutil cs revert BE1E… - paste in that long string in place of BE1E…

As always, ensure you have a backup in case things don't work out.