Regarding the Camunda Process Engine, yes, External Service Tasks represent transaction boundaries. However, I’m not really sure what is the case in Zeebe. You can ask on the official Zeebe forum here: https://forum.zeebe.io/ (or maybe @Philipp_Ossler knows more).
@Philipp_Ossler I know the architecture of Zeebe and the fact that is an external component. Due to the fact that the workers polling Zeebe for tasks is similar to the external task pattern of Camunda, I was curious if in fact also for Zeebe all the tasks represent transaction boundaries.