We have recently contributed a quarkus extension called quarkus-narayana-stm which simplifies the use of STM in your microservices.
It will be available in the 0.24.0 quarkus release. If you would like to experiment with it before this release then you can either take one of the nightly builds or you can build it locally by git cloning the quarkus repo and then run the build. This will add the io.quarkus:quarkus-narayana-stm:999-SNAPSHOT maven dependency to your local maven repository and you may then get started by following the guide. There is also a quickstart that provides a worked example of how to use it in your microservices. The example shows how to manage concurrent accesses to a single counter. More sophisticated usage patterns are the norm but this simple example does give a flavour of how easy it is to manage concurrency with the Narayana STM implementation.