(Steam) UI scaling does not work in FullHD

[zarremgregarrok]

Hi fellow Original War fans.
I recently bought the Steam version of our beloved old game and it seems to be struggling with scaling to fullHD.
While the UI scaling is present in the options, it is grayed out (and still editable), but does not change anything.

Is there something I need to make UI scaling work, or do I need to use the old resolutions and use monitor settings to prevent stretching?