It is simple LOL do not chase MP - do not buy a 4MP camera that is anything other than a 1/1.8" sensor. Do not buy a 2MP camera that is anything other than a 1/2.8" sensor. Most 4k are on the same sensor as a 2MP and thus the 2MP will kick its butt all night long as the 4k will need 4 times the light than the 2MP...4k will do very poor at night unless you have stadium quality lighting (well a lot of lighting LOL).
When we had a thief come thru here and get into a lot of cars, the police couldn't use one video or photo from anyone's system that had the 4k fixed 2.8mm or 3.6mm cams - those cams sure looks nice and gives a great wide angle view, but you cannot identify anyone at 15 feet out. At night you cannot even ID someone from 10 feet. Meanwhile, the perp didn't come to my house but walked past on the sidewalk at 80 feet from my house and my 2MP varifocal zoomed in to a point at the sidewalk was the money shot for the police that got my neighbors all there stolen stuff back.
In fact my system was the only one that gave them useful information. Not even my other neighbors $1,300 4k Lorex system from Costco provided useful info - the cams just didn't cut it at night. His system wasn't even a year old and after that event he has started replacing his 4k cameras with 2MP cameras like mine after seeing my results - fortunately those cams work with his Lorex NVR. He is still shocked a 2MP camera performs better than his 4k cameras... It is all about the amount of light needed and getting the right camera for the right location.