When trying to do anything else than selecting tiles, the mouse drag/ click will anchor from the bottom left corner - regardless of resolution, full screen, UI scale. Unfortunately, this makes the game unplayable.
This issue might be related to this:
Create a new world with default settings, try to mark anything for digging by hold clicking and dragging the screen to the bottom left. The selection will be made starting from the bottom left corner of the screen. Note that nothing will be selected if you just drag a selection without moving the viewport.