My Roku started flickering every 3 seconds this morning. It pretty much makes the TV unwatchable.
It was working well for the past 2 years until this morning when I turned on the TV by casting a youtube video from my Computer (which I always do and never had an issue before today).
I tried to reset, change the display settings and even did a factory reset but to no avail. I noticed that after I left the TV off for a few hours, when I turned it on again it didn't flicker for the first few minutes, and then it went back to the flickering every 3 minutes (made me think could it be a dust problem?)
Have you tried contacting the TV manufacturer to inquire further? I'd suggest starting there to see what options or suggestions they can provide. Each Roku TV manufacturer provides direct support and warranty services for their products running the Roku OS.
TCL's use cheap power supply boards with cheap chinese capacitors.
they start to exhibit display issues like blinking, flickering after 2-3 years.
Google shows that the most common cause of flickering in monitors and TVs is bad capacitors.
You can find a replacement power supply board on ebay for under $20. I know of one seller who sells tv parts and has a free return shipping policy if the part does not fix your issue. Just search ebay.
My TCL 43" 4k TV also started to malfunction after 2 years. I bought a replacement power board which fixed the issue for several months, but the problem has returned because of the cheap board components. I'm going to replace the capacitors with high quality japanese capacitors, and hopefully that will solve my blinking issue.
Another thing you can try before replacing capacitors or power board is to lower the brightness and set it to low power mode in the tv menu, turn off the tv, wait an hour, turn it back on and set it back to your usual brightness and power mode. May or may not work.