As both those previous issues have pointed out, it depends on themes.
Some themes are sized for HD screen resolutions, and then the handle size is fine for users to find, but if the resolution is QHD or UHD or finer then the handle may be far too small for users to easily find and use it.
It seems to be dependent on the way the theme is set. Some work perfectly well for me, both on an ancient HD laptop screen and a QHD screen. Perhaps these themes set the handle size as something that is not dependent on the resolution, or perhaps they load an image in the handle, but whatever that makes the themes pane handles usable on either system.
Perhaps if people have themes that are set badly they need to set the pane separator, but AFAIK there is no way Geany can include a setting for "crap"[^1] themes without interfering with "good" themes. AFAIK the only thing might be to include a commented out CSS entry in `geany.css` that users could uncomment if their theme is "crap".
@techee if Mac has a poor theme perhaps you could patch it for that only of course.
[^1]: technical term :grin: