Here is what a $1 ESP wifi dongle has to follow:
https://en.wikipedia.org/wiki/IEEE_802.11
"The mask requires the signal to be attenuated a minimum of 20 dB from its peak amplitude at ±11 MHz from the center frequency"
So 2 dB/MHz filter.
I let you do the math.
FAA is just ridiculous here if they let old junk radio hardware handle safety landings for airplanes, but well after 737 max what do you expect...
n.b. Wifi (and BT and others) got to use 2.4GHz band because of interference from aircraft kitchens causing a push to make 2.4GHz into junk spectrum with less regulation.
3rd ord IMD for non-EE could be described as low power mixers like mixing low power signals and usually the low power signal comes from your intentionally designed radio oscillator, but, whack it with enough incoming RF power and it will go non-linear as its designed to do and start mixing with that incoming signal, mostly making massive levels of interference. You can always improve 3rd order IMD by simply running the oscillator and mixer at higher power levels (which all turns to heat), usually not the best strategy for battery powered gear.