the workflow management module comes with Mendix 9 GA, presumably in spring time….
See the Mendix world presentation here: https://www.mendixworld.com/session/workflow-the-ultimate-springboard-for-intelligent-automation/
It is currently in Beta.
Workflows are not publicly available yet. I compiled all current information in this blog post: https://www.mansystems.com/blog/mendix-workflows-what-we-know-so-far