“Staring at a rout, Trump believes the polls, even if many here don’t.”
That’s a broad supposition. Could be that others advised him to do this. Could be that there are specific factors that make the new person a better choice. Further, to your point, why in the world would polls be more accurate now than they were in 2016? Why would anyone make that supposition?
As to why the polls may be more accurate now, I know that pollsters have corrected one significant predictor of voting preference since 2016, and that is education level. They are supposed to adjust for education level now, and did not in 2016, thereby missing a key Trump voting vector.
A second reason is that people are home, not traveling, etc. Easier to reach than in 2016.
As to whether there is a "shy Trump vote", I think yes, there is. There may be a 1-3% effect from this. But a double digit gap will be hard to overcome. Even Republican leaning pollsters (Gravis, Rasmussen) are showing Trump behind.