Richard,
That is an access door to the holding tanks, basement heater, and a lot of plumbing and electrical gear. You probably do not want to block it. Although it has 8 screws, they are into plywood and not very secure. If you have clearance , you may attach the TV mount to the ceiling or the wall to the left. Whatever your decision, make it removable for the access door. You may want to remove the 8 screws to inspect the area.
Larry