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.