It's been four years since the first AppleTV 4K was introduced, and there's still a lot of confusion regarding its video "Format" setting as well as "Match Content". So, here's a quick explanation of how these settings work, since the way Apple has configured it doesn't necessarily make a lot of sense.
The settings I'm addressing are under the menu General>Audio & Video.
I'm going to address the "Match Content" settings first. With systems capable of HDR (HDR10 and Dolby Vision) there is the option to turn "On" Dynamic Range. I suspect anyone with an HDR capable system will want to turn this on. That will make the ATV switch between SDR and the best version of HDR available for each individual program. Basically it activates the same process available with most UHD disc players. When the program you choose to watch has a form of HDR that is compatible with your system, it will automatically switch to that. If it is SDR, it will switch to that.
The second setting in the "Match Content" menu is "Frame Rate". If your display is compatible with frame rates other than the standard (in the US) 30 or 60 fps, this setting can also be turned "On", and generally should be. The main benefit is that film sourced programs can play back at their native 24fps instead of being converted to 30fps, which causes artifacts.
The greatest confusion is regarding the "Format" setting. Depending on your system, there can be a lot of options, but in the US there are three primary ones to choose from at the top of the list. These are "4K 60Hz SDR", "4K 60Hz HDR", and "4K 60Hz Dolby Vision" The "Format" setting determines what format the AppleTV outputs menus and screen savers only, when "Match Content" is turned on for Dynamic Range, as suggested above. So, most people seem to prefer setting "Format" to "4K 60Hz SDR" for several reasons. First, there's not a big benefit to viewing menus and screen savers in HDR, and it avoids a lot of switching back and forth between SDR and HDR, since most content is still SDR. Also, with an OLED display, needless use of HDR could have detrimental effects on the life of the panel. Some people just prefer the look of HDR menus, but most seem to prefer they default to SDR.
Apple has added something to the menu to make things even more confusing. That's the "Enable Dolby Vision" option that appears if the format is not set to 4K 60Hz Dolby Vision. In fact, any time the ATV senses a DV compatible system for the first time, it will prompt you to "Enable Dolby Vision". The problem is, if your system is capable of Dolby Vision and you have Match Dynamic Range turned "On", you DO have Dolby Vision enabled, even though it acts like you don't. It will switch to DV when the source material is in Dolby Vision.
I hope this clears things up a bit.
The settings I'm addressing are under the menu General>Audio & Video.
I'm going to address the "Match Content" settings first. With systems capable of HDR (HDR10 and Dolby Vision) there is the option to turn "On" Dynamic Range. I suspect anyone with an HDR capable system will want to turn this on. That will make the ATV switch between SDR and the best version of HDR available for each individual program. Basically it activates the same process available with most UHD disc players. When the program you choose to watch has a form of HDR that is compatible with your system, it will automatically switch to that. If it is SDR, it will switch to that.
The second setting in the "Match Content" menu is "Frame Rate". If your display is compatible with frame rates other than the standard (in the US) 30 or 60 fps, this setting can also be turned "On", and generally should be. The main benefit is that film sourced programs can play back at their native 24fps instead of being converted to 30fps, which causes artifacts.
The greatest confusion is regarding the "Format" setting. Depending on your system, there can be a lot of options, but in the US there are three primary ones to choose from at the top of the list. These are "4K 60Hz SDR", "4K 60Hz HDR", and "4K 60Hz Dolby Vision" The "Format" setting determines what format the AppleTV outputs menus and screen savers only, when "Match Content" is turned on for Dynamic Range, as suggested above. So, most people seem to prefer setting "Format" to "4K 60Hz SDR" for several reasons. First, there's not a big benefit to viewing menus and screen savers in HDR, and it avoids a lot of switching back and forth between SDR and HDR, since most content is still SDR. Also, with an OLED display, needless use of HDR could have detrimental effects on the life of the panel. Some people just prefer the look of HDR menus, but most seem to prefer they default to SDR.
Apple has added something to the menu to make things even more confusing. That's the "Enable Dolby Vision" option that appears if the format is not set to 4K 60Hz Dolby Vision. In fact, any time the ATV senses a DV compatible system for the first time, it will prompt you to "Enable Dolby Vision". The problem is, if your system is capable of Dolby Vision and you have Match Dynamic Range turned "On", you DO have Dolby Vision enabled, even though it acts like you don't. It will switch to DV when the source material is in Dolby Vision.
I hope this clears things up a bit.