The other guys answer is really good if you are out of warranty.
But this exact same thing happened to me and I just bought my TV 5 months ago. I called the company and they are sending a box and fixing or replacing the TV for free. Apparently this is a very common problem.
Are you still in warranty?
I'm going to search for some kind of extended warranty for it even though I might be out of luck because if this happened in December of 2020, to a TV that was manufactured in May of 2020, and purchased in July of 2020,.And then set up with all of the auto power off functions so it would not be left on for too long it will probably happen to a large swath of TCL TVs.
Lemons.