> Somehow reading a function name "toggle-tab-bar-mode..." my
> understanding is that such a function would enable and disable tab-bar
> functionality itself, rather than only show and hide the bar. I see
> now that toggling the 'tab-bar-mode' minor mode also does not
> enable/disable the tab-bar functionality, but rather seems to just
> toggle the actual bar. Is this correct?

This is almost correct.  Additionally, 'tab-bar-mode' also
loads button images and assigns C-TAB keys.

> If so, what is the difference between 'toggle-tab-bar-mode-from-frame'
> and 'tab-bar-mode'. Both of them seem to toggle the tab bar in
> _all_ frames.

Indeed, 'tab-bar-mode' toggles the tab bar in all frames, but
'toggle-tab-bar-mode-from-frame' is a very specialized command.
It's used only in the Show/Hide menu, to have the toggle reflect
the current frame, as the comment before its definition says.
Maybe this comment should be moved to its doc string like this:

diff --git a/lisp/tab-bar.el b/lisp/tab-bar.el
index 5a95e5975d..e239a02a64 100644
--- a/lisp/tab-bar.el
+++ b/lisp/tab-bar.el
@@ -187,9 +187,9 @@ tab-bar-handle-mouse
         ;; Clicking anywhere outside existing tabs will add a new tab
         (tab-bar-new-tab)))))
 
-;; Used in the Show/Hide menu, to have the toggle reflect the current frame.
 (defun toggle-tab-bar-mode-from-frame (&optional arg)
   "Toggle tab bar on or off, based on the status of the current frame.
+Used in the Show/Hide menu, to have the toggle reflect the current frame.
 See `tab-bar-mode' for more information."
   (interactive (list (or current-prefix-arg 'toggle)))
   (if (eq arg 'toggle)