The Telegraph article includes the actual video from Trump's Truth Social feed, instead of just vaguely alluding to it. Short version is it's video of a couple of pickup trucks covered in pro-Trump, pro-police crap, and the second one has one of those tailgate decals showing Biden bound and gagged that you sometimes see in very red areas.
That's what we're talking about, and there's no way it's not well within the bounds of 1A protected speech.