gmic cli: X11 windows with slider

Is there any way to create display windows with sliders?

I have images not fitting into the screen. In a custom routine I create windows (with ‘w0’ and ‘w1’ and custom event routine) which are cropped by the screen size. Maybe a help could be sliders?!

Another solution could be the use of the ‘display’ routine, still it seemingly does not allow custom event handlers or I don’t know how to catch them.

No, there is no such possibility.
Ultimately, it is possible to create your own custom viewer with sliders, but that’s honestly more than a bit of work to achieve.