While complacency is a valid concern, and I appreciate efforts to keep fellow supporters focused on the prize; I don't think its an issue Trump needs to worry about.
My reasoning: Trump voters, even if they think Trump will win, have more to prove than Biden voters. A Trump landslide, even if unlikely, is the best outcome for his supporters. People voting Biden just need to get Trump out of office; however narrow that margin of victory may be. Biden is running on a platform of "not Trump", and therefore his supporters gain nothing additional from an above-and-beyond victory on behalf of Biden that they wouldn't be getting from a by-the-skin-of-his-teeth victory.
Its the difference between the college students fighting for that 3.5 GPA to keep their scholarship, and the students just aiming for that 2.5 GPA to graduate.

The youth vote going to Trump because all the liberal youth are buttmad about Bernie cucking while the fence-sitters and right-leaning youth are fired up after Kavanaugh and Kenosha