The First Amendment does allow you to yell "Fire!" in a crowded theater. The 1919 Schenk case in which Justice Holmes gives that example was overruled by the 1969 Brandenburg case.

If you want more information about this, feel welcome to read: this Atlantic article, this Reason article, or this transcript of an interview with Ken White, a 1st Amendment lawyer.

Edit: More importantly, Trump's speech in the lead up to January 6th would be considered constitutionally protected unless it fit one of these categories:
1. True threat: Trump would have had to express an intent to commit unlawful violence to a particular person or group of persons.
2. Incitement of immediate lawless activity: Trump's speech would have to have been “directed to inciting or producing imminent lawless action and is likely to incite or produce such action.” I think this is debatable to the extent that a conviction for his speech on January 6th would almost certainly become a landmark Supreme Court first amendment case.

I am more curious as to why not only can someone look at all the evidence and not see Trump for what he truly is (a dangerous loser who embodies none of the qualities actually needed in a president), but why those someones number in the tens of millions? Trump will receive upwards of 75 million votes this November. Nearly or virtually half of the electorate will vote for him. Sadly, many being just as convinced that those who vote for Biden are voting for a dangerous traitor.

Somewhere we took a very wrong turn in this country and went down a dark and dangerous path. Whatever bad things that happen during this election season, and especially on and around election day and the weeks that follow (if anything bad does happen), none of it will surprise me. No matter what it is.