The email is currently mandatory.

There is at least one use case when the email is not desiderable:

I receive a Google Meet link with date and time by message in a Telegram DM or whatever.

The meeting is agreed upon and confirmed by both.

That person already has the event on his Google Calendar.

I want to set it on my Proton Calendar with the counterparty email as a reference for myself, but I would rather not send a duplicate confirmation email.