SSH Key Certificates

ok -- I get it suddenly working. With FreeBSD 13-systems it works; with older FreeBSD-versions it does not work and it also does not work with CentOS7-systems, but Debian 11 works.

My output from ssh -v:
❯ ssh -v desthost
OpenSSH_8.6p1, LibreSSL 3.3.5
debug1: Reading configuration data /Users/nik/.ssh/config
debug1: /Users/nik/.ssh/config line 204: Applying options for desthost
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 21: include /etc/ssh/ssh_config.d/* matched no files
debug1: /etc/ssh/ssh_config line 54: Applying options for *
debug1: Authenticator provider $SSH_SK_PROVIDER did not resolve; disabling
debug1: auto-mux: Trying existing master
debug1: Control socket "/Users/nik/.ssh/connections/mux_00e2d55221ac236fbe3807269258a4722b2647a7" does not exist
debug1: Connecting to my.destination.com port 22.
debug1: Connection established.
debug1: identity file /Users/nik/.ssh/id_rsa type -1
debug1: identity file /Users/nik/.ssh/id_dsa type -1
debug1: identity file /Users/nik/.ssh/id_ecdsa type -1
debug1: identity file /Users/nik/.ssh/id_ecdsa_sk type -1
debug1: identity file /Users/nik/.ssh/id_ed25519 type -1
debug1: identity file /Users/nik/.ssh/id_ed25519_sk type -1
debug1: identity file /Users/nik/.ssh/id_xmss type -1
debug1: certificate file /Users/nik/.ssh/id_rsa_sam-cert.pub type 4
debug1: Local version string SSH-2.0-OpenSSH_8.6
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.5 FreeBSD-20170903
debug1: compat_banner: match: OpenSSH_7.5 FreeBSD-20170903 pat OpenSSH_7.0*,OpenSSH_7.1*,OpenSSH_7.2*,OpenSSH_7.3*,OpenSSH_7.4*,OpenSSH_7.5*,OpenSSH_7.6*,OpenSSH_7.7* compat 0x04000002
debug1: Authenticating to my.destination.com:22 as 'user'
debug1: load_hostkeys: fopen /Users/nik/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: mailto:chacha20-poly1305@openssh.com MAC: compression: none
debug1: kex: client->server cipher: mailto:chacha20-poly1305@openssh.com MAC: compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: SSH2_MSG_KEX_ECDH_REPLY received
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:OHY8LPz3qv2cSwyMVIp/J32p38pin0cEbiMtAZXexhk
debug1: load_hostkeys: fopen /Users/nik/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: Host 'my.destination.com' is known and matches the ECDSA host key.
debug1: Found key in /Users/nik/.ssh/known_hosts:18
debug1: rekey out after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey in after 134217728 blocks
debug1: Will attempt key: /Users/nik/.ssh/id_rsa_sam-cert.pub RSA-CERT SHA256:jzuBd+ulgpxou9emJu1RRvIn9bf6plMl0E4mhQLHZvU explicit
debug1: Will attempt key: id_rsa_sam RSA SHA256:jzuBd+ulgpxou9emJu1RRvIn9bf6plMl0E4mhQLHZvU agent
debug1: Will attempt key: /Users/nik/.ssh/id_rsa
debug1: Will attempt key: /Users/nik/.ssh/id_dsa
debug1: Will attempt key: /Users/nik/.ssh/id_ecdsa
debug1: Will attempt key: /Users/nik/.ssh/id_ecdsa_sk
debug1: Will attempt key: /Users/nik/.ssh/id_ed25519
debug1: Will attempt key: /Users/nik/.ssh/id_ed25519_sk
debug1: Will attempt key: /Users/nik/.ssh/id_xmss
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,keyboard-interactive
debug1: Next authentication method: publickey
debug1: Offering public key: /Users/nik/.ssh/id_rsa_sam-cert.pub RSA-CERT SHA256:jzuBd+ulgpxou9emJu1RRvIn9bf6plMl0E4mhQLHZvU explicit
debug1: Server accepts key: /Users/nik/.ssh/id_rsa_sam-cert.pub RSA-CERT SHA256:jzuBd+ulgpxou9emJu1RRvIn9bf6plMl0E4mhQLHZvU explicit
sign_and_send_pubkey: signing failed for RSA "id_rsa_sam": agent refused operation
debug1: Offering public key: id_rsa_sam RSA SHA256:jzuBd+ulgpxou9emJu1RRvIn9bf6plMl0E4mhQLHZvU agent
debug1: Authentications that can continue: publickey,keyboard-interactive
debug1: Trying private key: /Users/nik/.ssh/id_rsa
debug1: Trying private key: /Users/nik/.ssh/id_dsa
debug1: Trying private key: /Users/nik/.ssh/id_ecdsa
debug1: Trying private key: /Users/nik/.ssh/id_ecdsa_sk
debug1: Trying private key: /Users/nik/.ssh/id_ed25519
debug1: Trying private key: /Users/nik/.ssh/id_ed25519_sk
debug1: Trying private key: /Users/nik/.ssh/id_xmss
debug1: Next authentication method: keyboard-interactive