I think the goal is just the general delegitimization of science and expertise. We are the only authority you should listen to. We are the sole source of truth and everyone else is out to fool you. Everything you hear otherwise is just a big coverup. They aren't telling you the whole truth. RFK and his anti-vax crowd are just useful idiots to that end. The Project 2025 types you mention don't give a fuck if anyone gets vaccinated or doesn't get vaccinated. As always, they'll be personally fine. But the more voters they can push into fearful, ignorant, and conspiratorial mindset, the more that they can spoon feed those voters "the truth".
It's the same thing that started happening with the media decades ago. Fox comes along and starts screaming 24/7 that everyone that's not Fox is woefully biased. You don't necessarily need everyone to believe that 100% (although plenty will, and do). You just need to get people to start thinking in terms of "two sides" to every story. If Fox implies "we're one half of the story", then people naturally start to believe that their local newspaper, the evening network news, the AP, etc is "the other half". So, boom, there's no referee any more. There's no common set of facts or common worldview that everyone is starting from. Now it just becomes a matter of can you tell a better story than the other guy? If you can, the details of that story don't even matter, because again, everything is two-sided, and if my story is crazy, then so is the other side's. I just need to present mine more persuasively.
But why stop with the media? That's only one piece of the wider culture. Now they've moved on to higher education, K-12 education, entertainment, science and medicine, and on and on. Politicize everything. Present two sides to every story. Confuse people as to what the facts are, and you've prepared their minds to hear whatever narrative you want to tell. Facts be damned.