gateway4 has been deprecated, use default routes instead

The message „gateway4 is deprecated, use default routes instead“ or „gateway6 is deprecated, use default routes instead“ comes from netplan and means the syntax has changed.

In the future, „routes:“ should be used for setting the default gateway.

Before:

gateway4: 10.225.192.1
gateway6: fe80::1

After:

routes:
    - to: default
      via: 10.225.192.1
    - to: default
      via: fd00::1

Then test the configuration with sudo netplan try and apply it with sudo netplan apply. That’s it.