Interesting. I've got a TCL 6 Series as well but have yet to upgrade to 4K. Maybe when I get around to replacing my PS4 with a PS5. Even so, my TCL is in the basement with east facing windows under a deck, so unless it's early morning it's pretty dark down there as a rule.
That's the one thing I don't like about my TCL 6 Series. HDR is so dark I pretty much have to watch 4K movies at night with the lights dimmed or off unless it's some super bright and colorful movie like Raimi Spider-Man or something.