It looks like mixed compilation with Java 8 and Scala 3.x (Scala 3.2.2 in my case) is broken.

The compilation fails with:

[INFO] compiling 2 Scala sources and 54 Java sources to /home/roman/dev/include-cloud/datacenter/target/classes ...
[ERROR] : 1.8 is not a valid choice for -java-output-version
[INFO] :   scalac -help  gives more information
[ERROR] one error found

The issue seems to be introduced by this change: ede3d72

The rough issue: -release 1.8 is added to the Scalac command, which it doesn't like. The ScalaMojoSupport.targetOption does translate the Maven 1.8 Java version to 8, but only for the Scala 2.x compiler series.

So, it seems that either the -release flag isn't correct for Scala 3.x, or the version translation should be applied to Scacal 3.x as well.