Colin Baxter <m43cap@yandex.com> writes:

> 1. Compile emacs-28 with gtk3 via ./configure <RET>
> 2. emacs -Q  <RET>
> 3. Evaluate (menu-bar-mode -1) in scratch.
> 4. Menu-bar is removed.
> 5. <F10> brings popup menu-bar.
> 6. Navigate popup menu with the mouse or arrow keys.
>
> Now repeat above steps for emacs-28 compiled with lucid. The popup menu
> can be navigated with the mouse, but not using arrow keys.
>
> This seems to have happened with emacs-28. It does not occur with
> emacs-27, where arrow keys can be used.

That's interesting, I see the opposite: it works in Emacs 28, but not
27.

0. emacs-27 -Q
1. M-0 M-x menu-bar-mode RET
2. <f10> <down> <down>

Nothing happens: