So proton really depends if its safe or not upon your traffic, if you're doing something illegal around the darkweb don't use protonmail because protonmail gives out user data upon request by federal facilities like FBI, CIA, DEA, instead you can use the following:
- DNMX Email
- SquirrelMail
- Anonymous Email
- Underworld Email
- RiseUp Email
If you're not doing anything illegal and just wandering around the darkweb in curiosity proton would be okay, as well as any of the listed above since BROWSING the darkweb isn't illegal so no one will get nosy behind you.