It's probably the rare TV hardware problem, not a common Roku software problem. You probably need to talk to the tv manufacturer for support (if it's still in warranty).
If not in warranty, google about it. Apparently these tvs only have 5 modules that are relatively easy to replace (can be bought on eBay maybe). There may be a video explaining how to do it, which module to try first. Could be that a ribbon cable (connector) needs to be reseated.
There should be a pinhole reset button on the back of the tv. You could try holding that down for 20 seconds and reset the tv. (I don't know if has to be on while doing that). If that doesn't fix it, then you probably have to do the above. One downside to trying this is, if it's a hardware problem that won't fix with a reset, then you lose all your settings. That might not happen if you re-seating the connectors fixed the problem, for example.
"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.