When I setup Tailscale on two different devices and have them chat, or have voice calls, via apps like Viber, does that mean that the chat/voice call is e2e (end-to-end encrypted)? If it is, would that also mean that Viber wouldn’t be able to read/listen to the content of our conversation?
Assuming that the voice traffic only goes between the two devices and doesn’t relay (and get decrypted) by the chat app’s servers, then yes.
To be specific, if the chat app decides to carry its traffic over
Tailscale, then Tailscale will provide the encryption. This works if
you use your own VoIP server, for example. You can also host your own
Jitsi server on your Tailscale network and do encrypted web
conferencing that way.