Enabling End-To-End encryption will require the encryption passphrase to be entered before acessing the passwords. See here how to set it up (recommended) or in the screenshot below.
It’s common troubleshooting for admins to uninstall and reinstall an app. If that would delete all data, it would be an unpleasant surprise for many admins. Users have the option to delete your data in the settings and admins via an occ command. Additionally, if a user account is deleted, the user data is also purged from the app.
Not sure if i understand you completely here. Do you mean that there is any extension out there that can sync the passwords stored in your browser to their own server? If so, do you have examples?