If you open Proton Pass and go to Profile and scroll down a bit it will tell you that this Device is not supported. Even if you enable Passkeys for third Party apps in Chrome, it’s still not supported.
As far as I understand it, it’s up to Fairphone to implement Passkeys into Android. Other Manufacturers like OnePlus or Oppo don’t have support either.
I am taking a wild guess here but I don’t think this Feature will be implemented in the next year because of the small Resources from FP.