To me, that is the strangest twist in this whole story: that Trump gets boo-ed by his supporters when he advises them to get vaccinated. They blindly accept everything he says, except for this one thing, which happens to be reasonable.
It's a key thing to keep in mind when considering his actions. He can rile people up in directions they're already leaning... He hasn't really demonstrated much ability to lean people in any particular novel direction, or against their pre-existing biases. He'll provide a focus to existing anger and say things that people don't want to say out loud, but he's as much a component of the overall anti-authoritarian, anti-establishment political wing as a leader of it.
Clarification: some of his supporters.
And how did he encourage the vaccines? We didn't have daily tweets saying things like 'TERRIBLE people opposing vaccines! SO SAD!!' He didn't really get behind them.
You can't spend four years supporting everything that undermines them, and then quietly say 'get vaccinated'.