Proton has an onion site for Proton Mail, (not sure if it’s for Proton VPN as well) but it’s a huge pain in the butt to sign up for an account. They often require email or sometimes SMS verification. Also, they redirect you back to the clear web page for the sign up process. It’s less than ideal. I use Proton Mail and I pay for it, so I also get Proton VPN but it only use it for torrenting. For all other things I use IVPN and I’m pretty happy with them. Customer support is great btw.