Description
Starting in Intel® Quartus® Prime Pro Edition software version 20.1, with the Selection Tool selected in the Block Diagram/ Schematic File, you can only select the objects in the GUI when dragging the cursor from top left to bottom right. Dragging the cursor into other directions will zoom in, zoom out or fit the block diagram.
Resolution
This problem is scheduled to be fixed in a future release of the Intel® Quartus® Prime Pro edition software.