Not sure what you mean. Changes to the interfaces in modular monolith are much easier than in microservices. You just release new version with updated interfac

Not sure what you mean. Changes to the interfaces in modular monolith are much easier than in microservices. You just release new version with updated interfaces - no need for versioning if you update interface and its usages. In case of microservices you must do versioning and either have to keep and support old version of the interface or spend some time to determine when to remove it.