Proton Pass currently only lets you use Simplelogin for email masking
but Bitwarden allows the use of many providers (addy.io, DuckDuckGo, Fastmail, Firefox Relay, Forward Email, Simplelogin)

Personally, although I have a Proton Unlimited subscription, my everyday mail provider is Fastmail and as such, I use their email masking feature.
They provide an API so it can be easily integrated to Proton Pass.

I'd really love to see this integrated