I have imported a link to my Google calendar into my Nextcloud calendar. It works fine - I now see my Google calendar.
But my Google calendar (in Nextcloud) does not seem to be automatically updated in the Nextcloud calendar when I enter new appointments in the Google calendar. How do I solve this?
The default refresh rate is once per day as described in the admin guide. If you want to rfresh it more often, adjust the update interval:
BTW, you can easily find answers on most of your questions by studying the admin guide or by using the search function of this forum (upper right corner) 
I don’t think I can access server settings since I only have a Nextcloud cloud solution (nx11)? 
try install the OCC Web app to enable occ commands from the web interface…
example calendar refresh every two hours
occ config:app:set dav calendarSubscriptionRefreshRate --value "PT2H"