IdentityAgent option has no effect about yubikey-agent HOT 2 OPEN

 IdentityFile
         Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA
         authentication identity is read.  The default is ~/.ssh/id_rsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
         ~/.ssh/id_ed25519_sk and ~/.ssh/id_dsa.  Additionally, any identities represented by the authentication agent will be used for
         authentication unless IdentitiesOnly is set.  If no certificates have been explicitly specified by CertificateFile, ssh(1)
         will try to load certificate information from the filename obtained by appending -cert.pub to the path of a specified
         IdentityFile.

         Arguments to IdentityFile may use the tilde syntax to refer to a user's home directory or the tokens described in the TOKENS
         section.

         It is possible to have multiple identity files specified in configuration files; all these identities will be tried in
         sequence.  Multiple IdentityFile directives will add to the list of identities tried (this behaviour differs from that of
         other configuration directives).

         IdentityFile may be used in conjunction with IdentitiesOnly to select which identities in an agent are offered during
         authentication.  IdentityFile may also be used in conjunction with CertificateFile in order to provide any certificate also
         needed for authentication with the identity.