A couple years ago there were some comments that the Apple TV 4K was only outputting 8 bit color. It was showing 4:2:2 at 8-bit color.(Apple TV 4K - HDR only with 8bit?) I am having the same problem. I noticed in the thread that someone mentioned they had and Optoma projector. I am experience this same problem on an Optoma UHD 50. I contacted Optomoa support almost a year ago about the issue. They said they were aware of the problem and were hoping to fix it in a new firmware update. Unfortunately, the COVID pandemic caused a lot of delays and now, a year later, I am concerned they will never push the update. So, if you do have an Optoma projector, please email their customer service. Maybe if enough people contact them, they will prioritize the update.
If anyone else has ideas or work arounds to fix this issue, please let me know. Thanks.