I am pretty sure that E2E encryption is impossible today if you are using a WebRTC SFU since there's no spec for it. The closest thing is PERC Lite [1] which no browsers support, though maybe you could cobble something together native.
WebRTC does not do signalling - that is the one part that you always have to provide yourself. WebRTC provides the peer descriptions and ICE candidates that you need to transport to the other party/parties.
Is there some path I didn't know about?
1. https://www.meetecho.com/blog/meetecho-and-cosmo-strike-agai...