The resolution (4k in this case) defines the number of pixels to be shown to the user. The bitrate defines how much data is provided in the file or stream. A codec is the method for converting data to pixels.

Suppose you’ve recorded something in 1080p (low resolution). You could convert it to 4k, but the codec has to make up the pixels that can’t be computed from the data.

In summary, the TV in my living room might be more capable, but my streaming provider probably isn’t sending enough data to really use it.