I discovered the save button, in fact. Never seen one of those!
But sync is still problematic. Last night I got a message on the mobile: "To allow Joplin to synchonise with Dropbox, please follow the steps below:
Step 1: Open this url in your browser... (etc)
Step2 Enter the code provided by Dropbox:
Enter code here."
But entering the url I was given in my browser produced this:
"Error (400)
It seems the app you were using submitted a bad request. If you would like to report this error to the app's developer, include the information below.
More details for developers
Invalid client_id:"
(shall I send you the code? Is this confidential?