Sources are by default "Public", they can be seen by all the users on the platform. You can make a particularly sensitive Source "Private".

If it's an existing source, go to the 'Sources' section, choose a source and click on the 'Settings' tab. Otherwise Start creating a new Source.

Go to "Privacy & Consent", Check the "Private Source" box and click on "Edit"

Now you are the only person able to see and follow this Source.