I can confirm the Thunar behavior but don't consider as a too big problem.
I can't or don't know how to test on Windows because I don't have a HiDPI screen in a VM but here a recent GIT master binaries: https://download.geany.org/snapshots/geany-1.39git20220109_setup.exe https://download.geany.org/snapshots/geany-plugins-1.39git20220109_setup.exe