The requirements to take the Expert exam are listed here. The 8500 XP points is no longer a requirement. You are required to have been the lead dev on a minimum of 5 projects, each time for at least 50 days.
For the portfolio, please include all your projects, not only the ones where you have been the lead. And yes, you can pick the project to discuss in more detail yourself.
After uploading everything, and everything is in order and all requirements are met, you’ll receive an email from either myself or my colleague to invite you for an interview. The combination of the interview and your documents will determine the success of your application.
I hope this answers your questions sufficiently and hope to welcome your application soon!
In addition to what Thijs answered: on that URL scroll to the ‘black’ part, there are all requirements stated.
The 8500 points requirement is not stated, but will be shown on https://academyportalcloud.mendixcloud.com/link/expertdeveloper
You can choose your own 5 (!) projects which you worked on as lead developer.