Yes, sometime over the last week or so I realized that 4 k was not working for the Prime video channel. I have a roku ultra on another monitor and no problems there and I am sure it did recently work properly as I watched several shows that rendered 4k HDR and verified as much.
I also have 2 fire tv ultra remotes and they work fine so its just with my TCL 8 65 in 2019 that this is occurring. The obvious thing for me to try is to install the previous update to the one currently being used
By the way, my current work around is installing my fire TV ultra on an open HDMI port but could really dig not having to keep an extra streamer on this tv. I also affirmed that my HDMI connectors were set to 2.0. I guess my most important question is how do I remove the latest update and put the previous one on?
Same issue here with my 8 series. A few others over at the 8 series thread at AVS are also reporting the same thing. They are saying it just started after the new firmware came down. I just got my 8 series yesterday, so I can't confirm the timing. All is working as it should on my P series, S series, and both of my 6 series sets.