Please be advised that each Roku TV manufacturer provides direct support and warranty services for their products running the Roku OS. Since your affected device is a TCL Roku TV, we suggest reaching out to their support team to report the issue and for further help.
Re: TCL ROKU TV 55S423, the top half noticeably turned dimmer than the rest of the screen.
I am having the same issue. Bought in Feb 2019 so I'm out of warranty, TCL support said "repair or replace". Called an electronics repair shop that said they can't do TVs. Some people are saying it happened after a software update, but my TV hasn't updated since May. I dunno, i just want my TV to not look like . Guess i'll go buy a better brand.