The latest version of the WebRTC spec introduces new promise-based methods for the RTCPeerConnection interface while keeping support for legacy callback-based methods. Some nonstandard uses of the legacy methods prevent the implementation of the new promise-based methods due to overloading conflicts and they are now deprecated. More specifically, calling createOffer() and createAnswer() without providing a failure callback (mandatory in the spec, but optional in Chromium) is now deprecated.
Docs: https://w3c.github.io/webrtc-pc/#legacy-interface-extensions https://developer.mozilla.org/en-US/docs/Web/API/RTCPeerConnection/createOffer https://developer.mozilla.org/en-US/docs/Web/API/RTCPeerConnection/createAnswer