I know. The issue is that it breaks mac standard key combinations
Yes, its a Linux binding, if "somebody" contributed Macos standard rebindings in a PR they can probably be included.
The only actual CSS posted was [5 years ago](https://github.com/geany/geany-osx/issues/14#issuecomment-544700194) but its missing the `-gtk-key-bindings` setting for filechooser that associates the bindings with the filechooser, see [here](https://docs.gtk.org/gtk3/css-overview.html#an-example-for-using-the-binding...) which might be why its doesn't work.