I’m in the UK too. My standard settings are:
4K SDR 50Hz
Match Dynamic Range: On
Match Frame Rate: On
Chroma: 4:4:4
I don’t have any issues with black screens when changing channels, but I just tried changing the Chroma to 4:2:0 and then I too get the black screen issue.
4:4:4 is the best quality setting anyways. Sounds like the answer.
My soundbar doesn't pass through 444 that's why I swapped originally, although that is not needed for me now. Still it's a bug that has been introduced on this version and may affect some people who can't use 444.
I can confirm 4K HDR 60 Hz if the frame rate match is on I get a black screen changing channels and going to the guide. Frame rate match is turned off all is good.
You will certainly have a mode change on your tv with those settings, as broadcast tv is not HDR.
You should run your Apple TV in SDR mode.
444 shouldn't be required for Apple TV content and many setups simply won't have the hdmi bandwidth for 444 to stick and could create other av issues
I have it on Match dynamic range and it only uses HDR if the content is HDR. the Samsung Q6FN has an indicator for when HDR is on. When I watch content from Apple TV + in HDR the HDR indicator goes on not for channels.