I have tried this on a pi 3b and a pi 4. I am using kali which supposedly comes with nexmon. I use the aircrack utility (airmon-ng start wlan0) and this creates a monitor mode interface. I try to monitor that interface and I don't see anything but beacons and spanning tree stuff. I have already run airmon-ng check kill to be sure that there are no processes stopping me from setting the channel.
I am sure that there is traffic on the nets. I have tried using WPA and open nets. I am running wireshark as root.
Other tools I have run (kismet) seem to identify the nearby nets from beacons but there is no evidence they see data packets that are non-broadcast (like a long ping). This mirrors what I have seen on wireshark.
I'm getting frustrated. I bought a pi 3b because I couldn't find an official statement of support for the pi 4. I see no difference in what I see.
If anyone has gotten it to work, can you tell me what you did? If I have to start over with a different distribution I will.