Platform authenticators (Windows Hello, Apple's Touch ID and Face ID, Android's screen lock) are reached through operating system APIs; roaming authenticators (security keys such as YubiKey or Titan, or a phone used through the hybrid transport) speak CTAP over USB, NFC or Bluetooth. Credential managers such as iCloud Keychain, Google Password Manager or 1Password act as authenticators for synced passkeys.
Capabilities differ: user verification method (biometric, PIN), discoverable credential storage limits on security keys (often 25 to a few hundred), supported algorithms (ES256 almost universally, EdDSA on many keys) and attestation. The authenticator data flags tell the relying party what happened (user present, user verified, backup eligible, backed up).