Catalina issue with External Sony 4K TV monitor

[abw2002]

Was working fine in Mohave. Now when booting, it flashes a rainbow of colors and never displays a picture. I have shut down and unplugged/replugged tv/monitor. Can't get a picture to come up on it. smh

 

[abw2002]

For my Mac Mini at least, holding down the power button for 10 seconds and booting up fixed it. I hope it is permanently and not a one-off.

 

[Dave_O]

There have been a lot of reports of this issue. Apple is aware of it, and is now advising Mac Mini owners not to update to Catalina. If the problem persists, a USB-C to HDMI adapter that handles 4K @ 60 HZ works for many.