One of the rooms in my house has trouble getting cool in the summer and warm
in the winter.

Someone told me recently to check the return air and make sure it is working
OK.

I did some checking. It turns out that even though a return air vent is
present in the room, it goes nowhere in the attic. I'm pretty sure that a
board (2x4?) covers the opening in the attic. Some years ago, I remember
drilling a hole in the board to feed a computer cable through the room
return air vent which is located near the bottom of the room wall.

The house is about 2200 sq ft, located in northern Texas. It has central
air conditioning. The air duct feeding air functions well.

Would the absence of a return air affect the temperature of the room?

Thanks for any replies.