Joplin sync target is Nextcloud.
I had to restore a Ubuntu server (on which the Nextcloud is running) snapshot.
Does Joplin sync the new notes, available on the client to the server? Or is the "source" the server, i.e. the new notes on the client will be deleted, because they are not on the server.
Missing some very import notes on my clients... Thats whay Im asking...
I think nothing will happen since the notes on your app are newer than those on the server, so it will just ignore what's on the server.
But you should consider sync broken at this point and the best would be fix it as described here, most likely by deleting everything and resuming from a JEX backup:
On none of my clients these important notes are anymore. All have synced already. And in the latest backup, these notes have not been included, they have been created afterwards