Passwordless without username with FIdo2 (through ldap authentification)

I would like to configure a passwordless authentification with Keycloak for a client/application. I would like to delete the username during the authentification. Only a security key with FIdo2 is required for users (except during the first connection to register the key). It’s possible with Keycloak with LDAP federation ?
Moreover, I can’t to have a password authentification option when I active WebAuthn Passwordless Authenticator for ldap users (it run when it’s locals users).
Do you have some solutions ?