Management UI -> Settings -> FTP Server
Set FTP server: Disabled then Apply.
Status in top right should show Status: Stopped
Click Dashboard then Reboot icon. Proceed.
Once back up, Settings -> FTP Server, Status: Running
Just upgraded to 6.7.0 from 6.6.6. Still in trial (28 days remaining...), active directory joined, no dockers, plugins, and one user share created.
That is as far as I've gotten, except to disable FTP and then reboot due to the ugprade...