What you see in that sample file is all you need to configure that static IP address. Do notice, you aren’t setting the address is the same fashion as you did with Ubuntu 16.04.

I changed the fixed ip address in network/interfaces on server XYZ, and "ip addr" reflects the change. I rebooted XYZ. I am able to ssh to the system using the new IP addr (192.168.1.1) . However ...

Here’s how you can configure different types of network interfaces using Netplan. Step 1: Identify Network Interfaces Before modifying configurations, identify available network interfaces using: ip a ...