Geany 1.33 was a GTK 2 build, but 1.38 is a GTK3 build, so probably there is some problem in GTK 3.24.30 on Windows 11.
Unfortunately there is no official testing of Geany releases on Windows 10 or 11, let alone on multi-monitor setups.
If you can build Geany on windows it would be great for you to test different versions of GTK3. I'm not a Geany windows user so can't help you with that, not sure if there is anyone who builds on 10 who might help, I doubt anyone does on 11.