Backlight went out in my 55" TCL Roku TV and since I'm past the 1-year warranty, TCL doesn't care. TCL TVs are very low quality. Roku should consider partnering with a better manufacturer. Very disappointing.
FWIW: There are some online tutorials/videos about replacing/fixing the backlight on TCL tvs.
I agree with you that they're cheap tvs. Onn too. I think Roku is hurting itself by trying to support such a wide variety of tvs (hardware). I think that leads to updates not being tested. Then waves of disgruntled customers complaining about how an update broke their tv. The whole thing (not just TCL) seems like an incredibly bad idea.
"People are often amazed at how much we’ve done with the number of engineers we’ve got." (Roku CEO Anthony Wood, Austin Statesman, Oct 4, 2019). "Amazed" is one way of putting it.