Error in log:
NoMethodError (undefined method `hash_function’ for an instance of COSE::Algorithm::EdDSA) lib/discourse_webauthn/authentication_service.rb:99:in ‘authenticate_security_key’
COSE algorithm Pure EdDSA does not have a hash function - therefore this error. cose_ruby does indeed have EdDSA support since October 2022. Details for using EdDSA can be found here.
I think the proper handling of this algorithm would be to call verify without a hash as recommended.