https://www.mendix.com/pricing/start-for-free/
The Mendix Free edition includes everything you need to design, build, and deploy demos, prototypes, or small applications. It includes a deployment environment for each application with unlimited users.
Good day,
To answer your question, you have different user types and according to your license type you will be restricted on that. Usually Mendix places a limit on the named users that your system can have. That is users with accounts that can sign in. They do enforce it on your system when it is running.