I've always thought that Trump nominally advocating for the vax was/is for persuasion purposes - it's very important that enough normies are turned against Brandon's side, or at least begrudgingly feel that "Trump wasn't so bad", before any drastic military action, or else there'll be no returning to a Constitutional Republic. As more and more Americans turn on Brandon, the targeted group becomes further and further left-leaning, and Trump has to espouse a vax opinion that doesn't immediately turn them off, sort of like not "coming off as racist". It's similar to how he came on very strong against illegals in the early part of his 2016 campaign, but later softened his phrasing a little to appease some American Hispanics, or came on strong with "you'd be in jail" against Hillary, but later appealed to her supporters for unity (which every president-elect does, but the point still stands), each time shifting his tone slightly to help capture a new group while retaining the old ones.