Hi,
thanks, I'm glad you found my article helpful!
I don't own any 4k camera, so I can only guess. I could imagine that there are apps supporting it - maybe even the IP Webcam app, did you try it and does it give you higher resolutions than 1080p in the settings?
Another point to consider is: for what use case would you need a 4k camera? If you just use it as a game live streaming camera showing your face in a small box, 720p is enough for example.
Also, many viewing devices won't even support 4k resolution.
Then there's the higher bandwidth usage both on the upstream and downsteam side...many things to consider.