How could even 36.9% of Americans hold a favorable view of an actual Nazi?
Because there's a lot of people in the US who either are Nazis or agree with their policies.
Nazis view other Nazis favorably.
The rest believe that someone in their "ingroup" cannot do any wrong. If they did something abhorrent it must have been a good reason or it's clearly a joke so they didn't mean it.
It really comes down to these people are brainwashed into thinking that someone like Musk is a genius/good person/role model. If he's got all of these "good" qualities how can he believe or something so incredibly evil? The answer is that they just shrug it off because he's "one of them" and because they believe they're a good person he must be too.