To delete the app is easy, but how to delete all other data? Where is it stored, in particular the database?
The database is stored in a directory linked to the app. If the app is deleted, so is the database.
If you are syncing the notes, the sync target is not deleted when the app is deleted.
But the Problem was the dropbox connection, which had to be disabled. Every time I started Joplin, new files came from dropbox, not from the database.
Well, you asked how to delete the app completely (with data), which means with the database. You did not ask how to disable syncing. I cannot read minds, I just answered your question.
Sorry, for telling the half question.
I wanted to switch from dropbox to Syncthing.
How to switch from Dropbox to “File system” (Syncthing)
With Syncthing ([https://github.com/canton7/SyncTrayzor](https://github.com/canton7/SyncTrayzor for Windows and https://f-droid.org/de/packages/com.github.catfriend1.syncthingandroid/ for android) you need no encryption, because it is built in and you can store as much as you want, for free. “Synchronizing” is also faster, because the files are stored local.
When you use Dropbox for syncing and you later want to switch to “File system” you first need to stop the dropbox-connection from your Dropbox account.
I’m not 100 % sure, but it seems if you delete Joplin and reinstall it you get the data again from the local Joplin Database, nonetheless. So then I had to delete the database by hand from the Apps Menu in Android and then I connect to “File System”.
Syncing Joplin with Syncthing works between Windows 10, Android and Linux.
Perhaps someone can improve this and put it in the documentation?