You should see 2.4 GHz noise floor when viewed from a spectrum analyzer in a densely populated, 5-floor, wood framed condo/apartment in a major urban area. Prototypical example would be some place in south lake union seattle.
Since 2.4 GHz goes through wood fairly effectively to moderate distances, it's a total half duplex CSMA hell...
One possible mitigation if you have older 2.4 GHz only devices is to run your own wifi on a 20 MHz channel, sacrificing throughput for better SNR. As channel sizes get narrower it cuts through the noise floor a little bit better. And of course to use your own choice of the cleanest 5.x GHz channel for everything you care about.
https://archive.curbed.com/2018/12/4/18125536/real-estate-mo...
https://crosscut.com/2015/04/the-new-seattle-where-everythin...
a "one plus five" looks like this, structurally: https://1.bp.blogspot.com/-DZ2BLyticQE/VRMjELb1DYI/AAAAAAAAX...
Since 2.4 GHz goes through wood fairly effectively to moderate distances, it's a total half duplex CSMA hell...
One possible mitigation if you have older 2.4 GHz only devices is to run your own wifi on a 20 MHz channel, sacrificing throughput for better SNR. As channel sizes get narrower it cuts through the noise floor a little bit better. And of course to use your own choice of the cleanest 5.x GHz channel for everything you care about.