Force a sync of iCloud Keychain from iOS to macOS?
This is how you can force an iCloud keychain sync as per Apple Support document, Get help with iCloud Keychain


  If you want to sync iCloud Keychain with other devices
  
  Make sure that your new device has the latest version of iOS and the latest version of macOS. Then, make sure that your device is on a Wi-Fi or cellular network. If the connection appears strong, try these steps:
  
  
  Turn off iCloud Keychain on all devices.
  Turn on iCloud Keychain on the device that has the most up-to-date keychain items.
  Turn on iCloud Keychain on your other devices. They will be updated with your new iCloud Keychain.