I tried Syncthing as you suggested.
I was only able to sync when I had a wifi connection at home, but it seems to have some advantages.
I don't seem to need syncthing's E2EE encryption because it trusts the registered devices that are interconnected (my local PC and smartphone).
My PC SSD partition has Luks2 encryption set up, so no problem... of course. I can't encrypt the Joplin data on my Android smartphone separately. Is it necessary?
With Joplin encryption turned off, it's a pleasant experience: frequent encryption/decryption is not required, which reduces synchronization time. (Does it clean up disconnected resource files even with encryption? Sometimes I feel like I'm running into trouble. I'm not sure.)
Compared to the Linux application Dropbox, Syncthing is lighter and seems to be better optimized. While the Dropbox installation files are not Foss, Syncthing can be installed directly from the Debian repositories. Syncthing is Berry Good.
But I think Android Dropsync is not bad solution. When someone needs Dropbox, Dropsync provides a seamless synchronization solution with Joplin. I also suspect that the dropbox stopping syncing issue might be related to encryption, but I don't know at this point.
At the time I was experiencing this, there were a lot of resource file errors that failed to decrypt when syncing from the mobile Joplin app. Could it be disconnected resource files? I don't know. If I manually removed the one resource file with the error, the decryption error in the mobile app went away by one line. In
I was at the time... I didn't want to see the error message, so I kept trying again and again. I would encrypt, then unencrypt, then set another encryption. Could this be the cause of a bigger problem?
Dropbox on mobile... Has anyone else had this issue without encryption?