Airplay mirroring, and direct plug in to watch movies from MacBook Air to Apple TV has stopped working

I have had my MacBook Air for 2 years, and have two third generation apple TVs. I have been using these devices to AirPlay mirror movies without ever having any issues. For the location of one of the Apple TVs, there is no wifi, so I use a HDMI to USB-C adaptor to play movies from my laptop on my TV.

This has always worked with no issues until the past 2 months. Initially I thought it was to do with my Apple TV, but when the same issue occurred on both Apple TVs it made me think it was my laptop.

Basically, airplay mirroring shows my laptop screen on the TV, but the minute I press 'play' on the movie, my laptop screen and apple TV turn black. You can hear the movie playing audio through the TV, but there is no image. I have tried all solutions listed previously - reset my apple TV, signed in and out of family sharing etc etc but nothing is working. My iPhone mirrors movies to my Apple TV with no issues at all, so it must be something at my laptop end. Thanks in advance.