Hi, I have a RPi 4B and I trying to using it with Airodump-ng and inmediately says "Fixed channel wlan0mon: -1"

On 5Ghz it can scan until channel 128 (5640Mhz). It is a hardware or software limitation? I'm using last Kali version and is all upgraded.

I can buy some adapter that works well, but I not known which works. Any recommendation?

I tried using "airmon-ng check kill" before and after scan with airodump-ng, but problem persists.