Ptm1545
There used to be a hidden menu with some additional HDR settings for TCL RokuTVs. (only works on some versions/models).
There are two variations for the below command.
Using the Roku remote, try pressing Home at least 5x, followed by Rewind, Play, Fast Forward, Play, Rewind.
Alternatively, try pressing Home at least 5x, then Rewind, Down, Fast Forward, Down, Rewind.
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When the above works, it should stay working until the RokuTV receives the next OS update. When that occurs, you may need to do the menu trick again. (that is, if this workaround is still working/available).
Many of the newer TCL RokuTVs are supposed to automatically configure itself for the best viewing experience, which many claim it doesn't, so users are left to the light, medium, and dark settings.