Thanks for the insightful answers. The issue was indeed PGTK, the official
build of Emacs 28 works fine. I didn't realize that the version I used was
not official, sorry.
However, the same issue still exists in Emacs 29 on Wayland and X (tested
on GNOME on both X and Wayland, using emacs-git with PGTK from AUR, which
compiles from development master branch), where PGTK is officially
supported. Based on your responses, it seems that this is a known issue,
but I cannot find any corresponding bug report (I could have missed it
though, I'm a bit clumsy with GNU's bug report logs). Should this bug
report be moved to Emacs version 29? Or should I report the issue again for
Emacs 29?

On Sat, 19 Mar 2022 at 15:18, Lars Ingebrigtsen <larsi@gnus.org> wrote:

> Po Lu <luangruo@yahoo.com> writes:
>
> > Are you running PGTK?  It's not present in the official pretests of
> > Emacs 28, but several very irresponsible individuals are haphazardly
> > merging the code from Emacs 29 into Emacs 28, and then distributing
> > packages labeled "enhanced or "wayland" on platforms such as the AUR.
>
> Well, it's free software, so people can do what they want.  But bugs in
> these Frankenstein Emacs versions should be reported to the people that
> distribute them, which in this case is Arch Linux.
>
> > The solution is to use the official build of Emacs 28, and to not use
> > PGTK on X Windows if you want to run Emacs 29.
>
> So there doesn't seem to be anything to be done on the Emacs side here,
> and I'm therefore closing this bug report.
>
> --
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no
>