Using external SSD as startup -- but can't rename internal disk

You could also try checking the box (in the image you posted, lower left corner) to "ignore ownership on this volume," rename it, then either use as is or uncheck that box again after renaming it. This is assuming you no longer plan to boot from that internal drive, since your boot drive is now the external one.

> "Rename" option in the Finder --> File menu is grayed out

You can not rename in the Finder Get Info dialog. You can rename in the Desktop or in the Sidebar after you have enabled the hard disks to display there in Finder Settings.

But notice that the Option-boot dialog might not display the new name. I recently heard that after a system update the new name might display. But the best practice is to format the volume in Disk Utility with a carefully planned name and let it be.

tjmacg wrote:

Thank you for the response. Unfortunately, none of these options work: I not able to rename it in Finder [the "Rename" option in the "File" menu is grayed out]; nor in Disk Utility [the name of the system volume is grayed out, the Data volume, which I was able to rename, as stated above].

I have no idea why you can't rename it in the Finder. I've never owned a Mac that I couldn't.

In Disk utility, you select the Volume Group and change the name in the Info pane to the right of the disk list.

You cannot rename the system volume by itself.

tjmacg wrote:

Thank you, although this also is grayed out for me. I presume there is some permissions issue that I have set incorrectly, but I can't figure out what or where that might be. I AM able up rename the "Macintosh HD - DATA" volume underneath, but not the volume group.

https://discussions.apple.com/content/attachment/e51848e6-5807-409d-bd2b-0f2529dcbe47

Either rename it in Finder (the drive, not Get Info), or in Disk Utility select the Volume Group and double-click the name in the Info window. Rename it there.

I definitely recommend @P. Phillips' suggestion to use Disk Utility since you want to make sure that both APFS volumes are properly renamed to avoid confusion. I find I must usually rename both the system volume and the Data volume separately. It has been a while since I have renamed them and don't recall if the Volume Group gets renamed, or whether it is easier to rename the Volume Group and if the name propagates to the volumes. It is crazy that macOS cannot do this automatically (Disk Utility actually worked this way for one version of macOS when renaming one of the two linked volumes, but later versions lost that feature IIRC).

In Disk Utilities in images

below

The Main Drive - Top Most Dire can not be re-named - First Image

The Containers below the Main Drive can be re- named - Second Image

What purpose with it serve if you re-name the Internal Drive

Rename files, folders, and disks on Mac - Apple Support (CA)

Excerpt from above link

Rename files, folders, and disks on Mac

You can change the name of most files, folders, and disks, including the internal hard disk (named Macintosh HD by default). If you change the name of your hard disk, it still appears with its original name on a network.