You changed how the UI scales, but you still didn’t properly trim all the elements?
In the upper left corner is a container/frame for 3 buttons: Main Manu, Objectives, and Recall, arranged from left to right. Within this container, there is also empty space: below the Objectives/Recall buttons and to the right of the Main Menu button. (either this is the case, or you added an element which has no visual representation or functionality and failed to remove it. Either way…)
You cannot click in the area defined by the lower and right edges of the Main Menu button, and the lower and right edges of the Recall button. This is because someone did not properly trim the container/frame that holds these buttons. As you increase the UI scale, this container increases in size, and as a result, so does the broken/unplayable area.
This makes twice that I’ve posted about this on these forums, and once on the Steam forums. It should be an easy fix. Snap to it.