I'm a teacher in Germany and at the moment I'm using the desktop version of Onenote, because I can use it with my Nextcloud, which is hosted in Germany.
I would love to use Joplin instead, but the sync with my Nextcloud is slow. Therefore I would be willing to pay for the Joplin Cloud, but sometimes I store pupils data and I can't save that informations on a Server located in the United States.
It would be really great, if the serverof the Joplin Cloud would be located within the European Union, so that me and others can use this service.
Joplin Cloud is a great product, but can't you achieve your goal of privacy by simply turning on encryption (no matter which syncing method you use)? As long as you've turned on end-to-end encryption you should be safe (if you don't put unencrypted copies of your Joplin folder on cloud storage by accident - e.g. by using iCloud for a device backup).
It should be even safer, though, if you used a Nextcloud server under your control for synchronisation (such as the one you're using right now). Joplin can do this via the WebDAV protocol.