I had a similar issue a few days ago.
I discovered that my aircraft was not parked correctly in the allocated spot. And if the aircraft is not in a proper position, the tug will not operate, it will only connect to the aircraft.
I just “slewed” the aircraft into the proper position, and the pushback tug operation went ahead smoothly.
The anomaly for me was, that I chose to start up at the gates (Cold & Dark), and by default, this was the position MSFS placed the aircraft in.