Hindsight is a wonderful thing.
Disrupting radio altimeters potentially prohibits the use of automatic landing capabilities, as used during bad weather when pilots can't see the airport.
The simple answer which should have been done when 5G was first mooted :- Test to see if there is any interference only on days when there is good visibility. Any pilot trying to blame interference on his radio altimeter when he can see the ground rushing up shouldn't be flying.
Yes I know that certain sizes of raindrops scatter radio in differing amounts and differing directions (otherwise weather radio wouldn't work), but presumably it does not affect the 4.2-4.4GHz band used by airliners' radio altimeters, otherwise they wouldn't work when most needed. Presumably this is how the frequency was allocated as you don't want an altimeter which gives a different result during weather. I would further postulate that the frequencies wouldn't have been chosen for 5G if there was a weather problem, 'cos the telcos would be seriously cheesed off if everyone phones up to say their phones don't work in the rain.