Protonmail is a widely used and common email provider. There is no reason why an employer would be prejudiced against your application based on you having a Protonmail address. I think a far more common thing employers think about when seeing applicants' email addresses are things like "haha, they're still using their email address from when they were 8 of alexdaboss at gmail dot com", but I highly doubt they care about what domain it's on unless you've got like a pornhub.com address or something.

seems like companies who know what proton is, would have no problem with it. some of their people would use it themselves.

companies who never heard of it wouldn't have any bad impression about it.

if they never heard about it but are wary/scared of everything they never heard of, might not be safe to work there. that's the kind of place that would test their workers' loyalty randomly, and not reciprocate any loyalty they receive.

My boss never cared about my disroot email. He just asked what is was

I use my own [email protected] (well actually it's last-net.com because I couldn't secure any better domain. It's too common.)

Never had an issue.

It's all good, especially now that they have proton.me when it was protonmail.com I had some issues saying it over the phone as some people didn't understand and it is long to spell.

Shouldn't make a damn difference! Ask this person to explain their thought process

Proton leaked a user's IP address to law enforcement, you should seek alternatives. source: https://arstechnica.com/information-technology/2021/09/privacy-focused-protonmail-provided-a-users-ip-address-to-authorities/