Can't turn off echo-cancellation on macOS

Troubleshooting guide for Can't turn off echo-cancellation on macOS in VDO.Ninja and OBS with likely causes and practical fixes.

I've had user reports that MacOS is forcing Echo cancellation on all devices except the built in mic. This was at least tested with a Scarlett Solo gen3 Any "extra" device has echo cancellation forced on currently. You can try forcing it off via the URL with &aec=0 or perhaps use a virtual audio cable. If you have added insights or solutions, please contribute them.