I was as surprised and disappointed as anyone, and I think we WILL take a few more steps backwards over the next few years, but I don't expect an unstoppable fall into fascism.
Most of the votes for Trump weren't actually FOR Trump. They were against the current situation they are in. They see him as the revolution. The anti-politician that will bring real change. They think all his court battles are the "Man" trying to hold him down and keep him from disrupting a system that gave up on its people long ago.
Of course that's all bullshit, but, assuming that all "normal" people can see through his lies and that only evil, woman hating racists would support him, is a big part of why he was elected.
Trump denied Project 2025 because he knew most people wouldn't want it. (Honestly, I would be surprised if he even knew what was in it) If he lets the Christian nationalists push that whole agenda on day one, he'll become the oppressive government that is taking away their freedoms. And nothing is more important to Trump than making Trump look good.
I'm way more concerned with Vance. Like you say, Trump does what's best for Trump. If Vance becomes President for whatever reason then ideology takes center stage.