You might be confusing it with netbird, which is the 601st implementation of a mesh network that does use both WebRTC and WireGuard.

There's no WebRTC in Tailscale.

Isnt a derp server juat webrtc with minor changes?

You don't need the whole of WebRTC for NAT traversal, TURN/STUN will do the job.

Edit: apparently it uses STUN/TURN but not WebRTC