I was using Geany 1.35 previously, on Windows 10.
Because of some features in the Window "Open file" dialog, I chose to use the windows dialog boxes. Mainly features like : renaming files, making copies, etc.
This option no longer works on Geany 2.0.
Native open/save dialogs were added back in https://github.com/geany/geany/pull/3861. You can try the nightly builds here:
https://nightly.geany.org/mingw64/
github-comments@lists.geany.org