UPDATE (04/04/2019): Google Play Store have now removed this notification.

The notification of the available Beta that is displayed on our App Page is a technical Beta that is being used temporarily, it is not the official Beta that is used for the Community Beta program.
Unfortunately, at the moment, we cannot accept any more Beta tester applications. We received many applications last round and we can only accept a limited number of testers.

Keep an eye on the Community Forum Announcements and look out for the next application round!

Thank you for your understanding on this matter and our apologies for any inconvenience that this may have caused.