Understood. Ok in that case, then only the 3CX Webclient will be able to potentially have a video call with that device.
In addition, some deskphones may potentially be able to have a video call with that device too (endpoint to endpoint).
And I say potentially, because H264 is not a single codec, it includes a subset of resolutions and bitrates so it is not guaranteed that it will work with WebRTC. It should work if there is a common "flavor" of the codec between the two ends, so you will have to test it and see how it goes. The same applies to 3rd party softphones. The PBX will carry the traffic but its ultimately up to the endpoint to be able to decode the stream.