Best to look at sensor size.
But better yet, what is the intended purpose for the camera? In many instances 4MP is more than sufficient and depending on what you are trying to accomplish, 2MP might be the better choice.
Lots of imitation 4K cameras out there put on 1/3" sensors that were designed for 720P or 1/2.8" sensors that were designed for 1080P
Once you chase sensor size and not MP, you will see the answers....
Most of the very good 4K cameras cannot see infrared, so you need available light or be willing to use the built-in white LEDs.
They also are not in varifocal lens yet, so their IDENTIFY sweet spot is 15ish feet.
4K should be on a 1/1.2" sensor or larger. That takes Reolink, Lorex, Amcrest, and any other consumer grade big box store out of the equation.
So you are left with Dahua and Hikvision models that are on the 1/1.2" sensor that are in the $200-$250 range.
There are probably a few others out there, but not many and probably more expensive.