A lot of human actions are unfalsifiable because we can't read minds. That why inference about what people say and do is important.

Musks and others nazi salute is just a reference to this behaviour writ large. It's not the beginning of it at all. Nazi and alt right groups have been doing dog whistles for decades, and the internet has proved a fertile ground for the behavior.

Its fine to not be aware of things like "88" or "14 words" or the like, but they are dog whistle memes used by racists and nazis, the people the mainstream right has been shifting towards for years and years. You very well may have some cultural touchstones that coincidentally use the same memes without that racist context, but when you're applauding the racists and using the terms at the same time?

Satre has a great quote about how facists dont care about what they say or do, as language is just a game to them:

Never believe that anti-Semites are completely unaware of the absurdity of their replies. They know that their remarks are frivolous, open to challenge. But they are amusing themselves, for it is their adversary who is obliged to use words responsibly, since he believes in words. The anti-Semites have the right to play. They even like to play with discourse for, by giving ridiculous reasons, they discredit the seriousness of their interlocutors. They delight in acting in bad faith, since they seek not to persuade by sound argument but to intimidate and disconcert. If you press them too closely, they will abruptly fall silent, loftily indicating by some phrase that the time for argument is past.

Jean-Paul Sartre

This game is wholley embraced by racists, so giving people "the benefit of the doubt" plays right into their game of feigning decroum while ramping up hate.

Again this may be an unfortunate coincidence for the proton CEO, but that does not undermine the overall point that he currently appears steeped in rightwing ideology, and that is not okay for someone claiming to uphold freedom and privacy.

Lastly, Protons past donations are laudable, but plenty of groups had laudable donations before they became vile. Look at google's past philanthropy as an example, or their since retired "dont be evil" motto. They certainly don't live up to those standards today, and it looks like Proton is on the same course.