Maven build with multiple Java versions

Imagine, you are tasked with maintaining a Java application that needs to run on more than one Java version. You want to ensure that it compiles, tests and builds on all of them. This is our story, buckle up, there are a few moving parts
This is a companion discussion topic for the original entry at https://wissel.net/blog/2024/04/maven-build-with-multiple-java-versions.html