User must specify

A description of what information recipients can enter for a presentation

You can ask the recipients of your Presentation to fill in information about themselves. Typically, this is used in relation to Questionnaires and subsequent Statistics. In addition to the 4 fixed ones such as Name, Company, Email and Birthday, you can create up to 5 more.
If you want to provide anonymity, you can simply refrain from setting these.

Here it is chosen that the user only needs to fill in Birthday. Likewise, there has been a period where the Presentation did not have any criteria, so the users there have been anonymous