There is a setting for disabling realtime channels over iroh because they are p2p and thus expose the IP addresses of the chat participants to each other (needed to establish direct connections).
WebRTC is something different, it is an API that could be used get internet access. As of right now there is no official way to disable access in chromium webviews, which is why we need the FILL 500 workaround on android and electron to block creation of WebRTC connection, by filling up the 500 connections limit which chromium has hardcoded.
This is what the annoying loading bar is about that you see when webxdc apps start up.
iOS and the new experimental Delta Chat desktop Tauri edition do not have this problem because their platforms provide a more reliable way to make the WebRTC APIs inaccessible.