You are probably approaching it in the wrong way.
The system is based on Contact & Account records (including the security model). The linkages (relationships/lookups are not on name, but the records GUID).
What you really want is rather than an email address, is a Contact record e.g. Contact Lookup (that you will populate with the Primary Presenter's contact record - i.e. your Primary Presenter should be a Contact).
When a user is registered, if they were invited the system automatically links them to their contact record (or if no contact creates a Contact record for them) i.e. User == a dataverse Contact.
You can actually run the query that you are currently trying to but not using the standard list etc, you can do it using either Liquid fetchxml, Portals Web API or Power Pages Flow, so its not that you can't get the data, its just that you will need to manage the presentation of the results rather than using the standard List or forms.
Edit: I am unclear on what your actual use case is but based on this statement "I'm asking on the form for the email so when a person registers for the PowerPages site, it will match up with their email." I would create a Contact in dataverse for the Presenters and then use the Send Invitation functionalty to send them an email to register. Also, depending on the authentication provider you are using, you may also find an advanced power pages setting exists (e.g. their is one for Azure/Entra) to use automatically match a registration to an existing contact using the email address (but for this to work you need to be sure email addresses are unique and that you won't accidently link to an incorrect Contact record).
