@fred There is no refresh button. The button enqueues synchronization, which is something different than refreshing collections. See here for more info: https://www.davx5.com/manual/accounts_collections.html#refreshing-the-collection-list
App for Calender & Tasks
What app can you recomand for syncing nextcloud Calender & Tasks
Is there an App that have both possibilities?
Best an App which is available for Android and iPhone
Hope for Help
The only app we know supporting both is acalendar+, because they implemented “Open Tasks”. I don’t think they offer an iPhone version.