Look at home>settings>system>system update. It will tell you the date the tv's software was last updated. Did the problem start on that date?
Something you could try is holding down the pinhole reset button on the back, to do a factory reset. You can do that from the system>advanced menu too. But, maybe the hardware reset would do something more. It's not clear how that button should be used. You might unplug the tv, hold the power button to discharge residual electricity, leave it unplugged overnight (or however long you can. Half an hour?). Hold the pinhole button while plugging in the tv. Continue holding it until the front light flashes (maybe 20 seconds). The instructions say to hold the button without doing anything else. But, I've read posts where people talked like unplugging did something more. Could just be superstition.
During the setup you should be able to see if the screen looks normal. If it looks normal, but then goes bad after setting up the network (and it downloads the latest updated software), you'd think it's the software causing the problem. But, if it looks bad as soon as the setup starts, it's hardware.
If it's hardware, there's a lot of people who have dug into these these things (replacing one of 5 boards). You might google about how to fix white screen. There's videos and blogs.
"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.
