I never personally believed he wasn't stupid. He's clearly a genius and a visionary in some areas (and probably a fair bit smarter than Trump, although that's a matter for debate).
But no one can be a genius in every area. Plus, intellect is arguably separate from values. You can be a genius and still be a bit of a douche (or even very evil/psychopathic, as history and Hollywood have shown us). Not saying he himself is evil or psychopathic btw; just pointing that out.
He made what looks to almost everyone (including one or two leading experts on Nazi history) to be a classic Nazi-style/far-right salute, then feigned ignorance. It's disingenuous at best.
Even if it was genuinely not intended to be one (as he claims), which is admittedly possible, the fact remains that that is how it looks to millions of people across the globe, whether they're misinterpreting him or not. It's not a good look, at any rate.
As an extremely high-profile individual with a LOT of cash and presumably access to the best PR advisors money can buy, it's not the kind of careless mistake you'd expect tbh.
So my own money's on him knowing full well what he did, either because he genuinely wanted to make a secret (or not-so-secret) dog whistle signal, or to meta-troll people because that's one of his hobbies, or for some other reason maybe only he knows.
Also please ignore my extra-word typos (glitchy phone).