It seems you’re misusing the desktop client.
The desktop client assumes you’re using your own computer account with your own user and password. Nobody should see your personal files unless you explicitly want.
If you’re using an account shared with multiple people, I don’t think the desktop client is prepared for this scenario.
Note that even if you logout, if the account is shared, people will still can access to the downloaded files, and could potentially override those, which would likely cause the desktop to upload the changes the next time it syncs