I am trying to write a Python script with Selenium to see if I can automate the registration process for a sample event I created. Here is the event page:

Your code steps would be :

1. Click on that Join the guestlist Button
2. Switch to Iframe. i.e driver.switch_to_frame("overlay_window")
3. Interact with your element or dropdown as per your requirement
4. Once you are done with all your operation with popup, Switch to default content i.e driver.switch_to.default_content()