Welcome to the Airtable community!
Do you have a PRO subscription, and did you enter the email associated with that subscription? In general, only people with PRO subscriptions are eligible to participate in betas. If you have a PRO subscription, you could try contacting Airtable support to inquire about the status of this particular beta.
As for this particular beta, I don’t know the full details. Having a PRO subscription does not guarantee access to any particular beta. And I don’t know if this particular beta is still active or not. However, the form that you linked to looks a bit simpler than most of the beta signup forms that I’ve seen recently. Usually they ask for a bit more information such as your experience with Airtable, how you anticipate using the beta, etc.
If this answer gives you enough information to solve your problem, could you please mark this post as the solution?
If not, could you please give a bit more details on your use case?