[Vinniess]

Is proton mail really secure and should they be trusted with your online data?

[GoodGuy3]

Yes and No. If you do something super illegal on their services, then yeah, they will give you up to protect themselves.

[Unknown]

It really depends on your threat model. What in particular are you worried about?
For most people, their services are totally fine. I even run a protonmail address as my primary email.
If you value privacy, they definitely have an advantage over other services like Google or Microsoft/Outlook.

If you're worried about privacy in your email communications, you should look into using PGP/GPG.
Regardless of the email provider, when using PGP your communications will remain private.

As GoodGuy3 had mentioned above, there was a recent case of proton giving up user data to law enforcement with a subpoena. Short of law enforcement requests, your data is likely as safe as any other provider.

Another service to consider is TutaMail. They're another private email service, very similar to proton. While I haven't seen a particular reference to them having given up user data to authorities, that's likely due to it being an overall smaller (less mainstream) platform.