This topic was about the sharing functionality not working (because the outdated sharing engine of GhostCloud breaks things).
what you’re asking for is automatic synchronization, which unfortunately is not part of SailfishOS’s Nextcloud integration, yet.
See this topic for example. You can search the forums a bit, there should be some feature request that you can upvote
As a side note: There’s a certain ‘confusabilty’ involved here regarding sharing files with Nextcloud. See more about that here: Sharing concepts: SFOS vs. cloud accounts