Please let me know if you find anything. I too searched online looking for a way to fix this. I accessed the secret menu only to discover no option for turning HDR on or off. Some darker scenes on Netflix and you are basically staring at a black screen with audio only. Another TCL Roku FAIL to add to the list. I've had my tv since Christmas and the list is getting loooong.
I have yet to find any info on this, unfortunately. Nor get any type of response. I too, am having issues with black crush, especially on Dolby Vision. It's really content specific, but the way the r625 local dimming is, it's really aggressive in certain scenes. I'm really hoping for a fix for this, but I'm sure they've long moved on from this TV. I honestly just wanted to play around and see if HDR10 was as bad as Dolby Vision, as Netflix has no option to turn it off.