Finally I found the cause of the problem. It was an old Autohotkey script
that I installed several years ago and forgot about it. I can not
understand why it caused problems only on Emacs 30. Sorry for bothering you

вс, 31 авг. 2025 г. в 14:34, Eli Zaretskii <eliz@gnu.org>:

> > From: Alex <al2255668822@gmail.com>
> > Date: Sun, 31 Aug 2025 14:08:51 +0300
> > Cc: Po Lu <luangruo@yahoo.com>, 79348@debbugs.gnu.org
> >
> > A: Dragging with the mouse the mode line between two windows does not
> work.
> >
> >
> >
> > Works as expected:
> >
> > Interactions with the menu (File Edit Options …)
> >
> > Interactions with the scrollbars
> >
> > Resizing frames
> >
> > Hovering over elements changes the mouse cursor, shows tooltips and
> feedback.
> >
> > Switching between frames via mouse clicks inside frames works as
> expected, but switching between windows
> > by mouse clicks inside a frame does not work.
>
> T^his basically means that the mouse works only when the click goes
> directly to Windows.  Any click or drag that should be processed by
> Emacs doesn't work.
>
> > Q: In "Settings -> Bluetooth & devices -> Mouse", review all the
> settings, especially the ones in "Additional
> > mouse settings".
> >
> > A: Reviewed. Standard mouse settings
> >
> >
> >
> > Q: Can you try with a different mouse, like a simple optical mouse
> connected via USB?
> >
> > A: I tried with a simple optical mouse connected via USB (Logitech). The
> situation is the same
>
> So this must be something system-wide, not specific to the model and
> make of the mouse.  Hmm...
>