Sync and alerts Nextcloud 17

Hello good afternoon
I would like to answer two questions.

1 - How can I sync my calendars with Google Calendars?
I’ve already set up inside Google Calendars and inside Nextcloud Calendar (Google appointments don’t show up in Nextcloud and Nextcloud shows don’t show up in Google)

2 - When I select the email alert, this message appears (Email reminders have not yet been implemented on the CalDAV server, so none will be sent.)
How can I adjust?

And also the alert via Popup does not work.

And finally, you refer me a good application to receive and view this calendar by phone?
I have an Android

Many thanks friends.
And sorry if this question is duplicated with another, I checked the cases here and found no similar ones.