The tooltip shown by toolbar drivebuttons is generated by Windows and can't be changed.
AFAIK Opus 12 was the same. Windows itself may have changed over the years.
(The similar tooltip for drives in This PC can be changed, via Settings > File Types. But that isn't what the toolbar buttons use, unfortunately.)
Lxp's suggestion to add labels to the drive buttons command will get you the labels on the buttons themselves, so they're always visible. (Won't affect the tooltips.)