Altimeter Band : 4.2Ghz - 4.4Ghz
VZ and AT&T agreed (long ago) to reduce power and stay inside 3.7Ghz - 3.98Ghz once the full deployment was done, staying 200MHz away from altimeters.
In Japan, they have been running 5G for over a year now up to 4,1Ghz, and restarting again at 4.5Ghz. Only 100MHz of guard on either side of the altimeter band. I think EU is close-ish, but not totally sure.
I can't find a single report or study that has shown radio altimeter issuers in Japan since 5G was turned on there.
Aside from a single study which a LOT of smart people have called out flaws in, there isn't much out there that proves there WILL be interference with altimeters, just a lot of FUD that says it MIGHT. I dunno what the angle is, but this has turned into a shitshow.