I was trying to make a simple aesthetic change to tab-bar to highlight a
tab when it is moused over.  mouse-face seems to work in tab-line,
header-line, and obviously in mode-line.  Mouse events are processed in the
tab-bar window.  Am I missing something obvious?  I tested in 29.4 and in
master.

emacs -Q -l tab-bar-mouse-face.el

tab-bar-mouse-face.el:

(tab-bar-mode)
(defun my/tab-bar-tab-name-format-function (tab i)
  (propertize
   (tab-bar-tab-name-format-default tab i)
   'mouse-face '(:inverse-video t)))
(setopt tab-bar-tab-name-format-function
#'my/tab-bar-tab-name-format-function)

-Stephane

P.S. I searched for a related bug but did not find one so this could be a
duplicate bug report.