Hi all, Short Answer Resetting NVRAM solved the issue for me - https://support.apple.com/en-us/HT204063 Hope it works for you, even though I saw a note here saying it didn't work for one person. It's super annoying if you're used to twin displays. I'm not a developer, but I came here searching for answers why macOS Big Sur 11.0.1 broke my HDMI to my Panasonic TV (Apple Thunderbolt Display always worked). Would not even detect that I had the TV screen. It was working fine with Big Sur 11.0.0, but I don't know when the autoupdate to 11.0.1 happened. What Didn't Work Rebooting several times Connecting/reconnecting HDMI cable at Mac mini/TV end Changing HDMI cable Connecting/Reconnecting to different HDMI port on TV Plugging HDMI lead into a separate Thunderbolt 3 port adapter and rebooting Resetting SMC (remove Mac mini power cable for 15 seconds) - https://support.apple.com/en-us/HT201295 My Setup Details Mac mini 2018 3Ghz 6-core intel core i5 2017 Panasonic TV TH-43D330M 1080p @60Hz 27 inch Apple Thunderbolt Display - connected via Thunderbolt 3 port adapter Run system as dual display