In a previous project, I encountered a similar requirement and implemented a solution using the searchable selector widget (Reference Set Option) for multi-select functionality. To dynamically populate the options in subsequent searchable selectors based on the selection in the first one, I utilized XPath queries to retrieve the relevant values. This approach effectively met the project's requirements and ensured a streamlined user experience.
Reference Widget : https://marketplace.mendix.com/link/component/116917