I've noticed that Proton Pass uses a basic password meter to determinate if a password is secure, like the classic "mix lowercase, uppercase, numbers and symbols" algorithm.

I suggest changing that with the zxcvbn algorithm developed by Dropbox instead (I personally recommend the zxcvbn-ts library). In this way, Proton can really tell if a password is secure enough, instead of relying on the classic and obsolete password strength algorithm.