The GDK_RIGHT_PTR cursor is provided only by GTK - there's no native Windows cursor of this shape so GTK renders the cursor by itself from the cursor theme bitmap. The code doing this is apparently buggy and does not take into account HiDPI screens so on a screen with 300% scaling, the cursor is 3x smaller.
Workaround this by using GDK_HAND2 which maps to a native Windows cursor that doesn't suffer from this problem.
See https://sourceforge.net/p/scintilla/bugs/2460/ You can view, comment on, or merge this pull request online at:
https://github.com/geany/geany/pull/4204
-- Commit Summary --
* Workaround incorrect scaling of "reverse arrow" cursor under Windows and HiDPI screens
-- File Changes --
M scintilla/gtk/PlatGTK.cxx (6)
-- Patch Links --
https://github.com/geany/geany/pull/4204.patch https://github.com/geany/geany/pull/4204.diff