It seems related to Quarkus defining the Antlr4 version as part of the whole ecosystem here:

https://github.com/quarkusio/quarkus/blame/c41872f2d3a1ecf97245c7f0eaaa4a18c658b07f/bom/application/pom.xml#L3252-L3261

in order for some MongoDB/Panache support, but with the side-effect of imposing the Anltr4 version for any Quarkus-based extension, including our kogito-quarkus-decisions.