I've used a Samsung 4K TV as a monitor on my Mac Mini for close to a year with no issues. After updating to the released version of Catalina, I would get a blank screen on my TV with the No HDMI Signal message from the TV. I could login into the mac via an iPad with Jump Desktop and the Mac had booted ok. Tried the standard stuff, HDMI cable swap, NVRAM, SMC but no help. Once in a while, often with a wired keyboard attached, the Mac would recognize the TV and display properly.
I had a CCC Clone disk for backup. When I booted from it, no issues at all. Awesome job by the CCC folks to have a video online showing the special steps needed to restore a Mojave Clone to a Catalina disk.
I restored to Mojave, and the monitor issue vanished.
EDIT - Downgrade to Mojave did not solve it. Suspect Catalina updated Mac HDMI firmware, which cannot easily be undone. I ended up getting a USB-C to HDMI cable which is a viable workaround. Others are reporting the issue as well. See - https://discussions.apple.com/thread/250715830?page=1
I had a CCC Clone disk for backup. When I booted from it, no issues at all. Awesome job by the CCC folks to have a video online showing the special steps needed to restore a Mojave Clone to a Catalina disk.
I restored to Mojave, and the monitor issue vanished.
EDIT - Downgrade to Mojave did not solve it. Suspect Catalina updated Mac HDMI firmware, which cannot easily be undone. I ended up getting a USB-C to HDMI cable which is a viable workaround. Others are reporting the issue as well. See - https://discussions.apple.com/thread/250715830?page=1
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