So, instead of Wireshark (and libpcap) reporting that monitor mode isn't supported, it lets you turn on monitor mode, but your capture doesn't show anything. the way they do that is not to 1) fail to report 802.11 DLTs when you ask for the DLT list and 2) report an error if you try to set the DLT for a BPF device bound to a Wi-Fi adapter to an 802.11 DLT - they just let the capture continue but don't provide any packets.

Apple may have decided to protect users from unintentionally deassociating from their Wi-Fi by refusing to go into monitor mode with those adapters.either newer hardware doesn't support being associated with a Wi-Fi network ''and'' being in monitor mode at the same time, or makes it difficult enough that Apple didn't bother supporting it in their drivers (or it's not hard but the Airport group at Apple couldn't be bothered to make the effort to support it) - older MacBook adapters, such as the one in my older MacBook Pro, supported it just fine, but it doesn't seem to work on my new MBP.On newer hardware, Catalina's support for monitor mode sucks. Tl dr: you'll probably have to deassociate from - meaning 'disconnect from' - your Wi-Fi network in order to capture in monitor mode.

Turn on wireshark packet sniffer