Non-exportable keys need backup paths
Keys locked in one Mac's secure enclave vanish with the hardware, so you need a second key registered elsewhere or another way into your hosts.
One key per device is correct
Several commenters argue keys should never leave the machine that made them; give each device its own key plus a hardware backup so revocation stays fine-grained.
Syncable alternatives are preferable
Others prefer 1Password, YubiKeys with backed-up GPG keys, or Trezor-derived keys so they can be recovered or shared across machines.