There just seems to be a massive disparity in the standards people expect from Trump and Harris (and I suspect that's down to sexism).
Harris is not a great candidate and does not always give particularly insightful answers. From her better moments, and her CV, it is plain as day that she isn't "dumb", though.
Trump mostly talks incoherent nonsense, clearly lacking even a baseline understanding of various issues, nor does he have the curiosity or capacity to learn (he famously would not read briefings prepared for him). If any other candidate, particularly a woman, cut short a Town Hall event an hour early, deciding instead to dance badly to random music for an hour, their career would be immediately over.
And sadly, that he seems to be one of the least intelligent people to ever hold high office is not even his worst characteristic.
I do suspect he'll win, though.