if the MOM gets a new version, do we just update the introscope.agent.connection.compatibility.version=10.7?
Release : 20.2
Component : APM Agents
You would not update that property, you would comment out or remove the introscope.agent.connection.compatibility.version=10.7 property.
Also, upgrading an EM (MOM and Collectors) from 10.7 to 20.2 is not supported. You must deploy from scratch. Here you can see all the information regarding the architecture, sizing, steps and etc:
Also, check the compatibility guide to determine the supported components: