I was setting up a laptop with FreeBSD 12.1-RELEASE and the installer set the regulatory domain to FCC4, I noticed it didn't show any 5Ghz networks.
I switched it to FCC3, and suddenly there were 5Ghz networks.
I thought it might be a driver bug specific to iwn but it turns out that it happens on my RPI3 with a ral USB nic.
I mentioned this to a friend who's very familiar with WiFi stuff on FreeBSD and he mentioned that this sounded like a channel list issue.
I also realized finding info/documentation about the regulatory domain stuff on FreeBSD was hard, so I just started digging into the source tree.
I read through src/lib/lib80211/regdomain.xml and I noticed the stanza for FCC4 had no entry for <netband mode="11na"> wheras FCC3 had an entry.