Generally support versions stated are the versions that have been tested and certified. But that doesn't mean it won't work with newer versions.
Did you run into a problem with a newer version of Mule?
Have you considered switching to our flagship product Dynatrace? It is certified to support Mule 4.2.0. https://www.dynatrace.com/support/help/whats-new/release-notes/oneagent/sprint-193/
Also remember that AppMon will be EoL in March, 2021.