Sure, this can get done. Find out what happens when you click the button ‘Save’ on your registration-page. Set a breakpoint in the microflow that you expect to get triggered, and see if clicking ‘Save’ indeed gets you there. From your description I expect ‘Save’ to either fail reaching the breakpoint, or fail creating the useraccount.
Btw. if you have ‘Administration’ in your AppStore-modules then to avoid confusion, tech debt and other bad thing, remove it, replace it by SystemManagement, making stuff like this easier. If you want to store extra user-info: consider module Person.
*Editted* In Mendix Studio Pro in a microflow you can rightclick any activity (for instance “Create New Account”) and select “Add breakpoint”. As soon as your app, while it is running, finds a breakpoint on its path, it stops an waits for you. See https://docs.mendix.com/howto/monitoring-troubleshooting/debug-microflows-and-nanoflows for more detailed explanation.
Also, smart to share the microflow, because now we can see the problem: it does too much and not the right things. All it needs to do, is ‘Commit’ your inputparameter ‘CreateAccount’.