Fantastic build! Everything works great, except wifi. I can't even get 40 MHz reliably, while 80 is right out. And it's stuck on 802.11n speeds. This despite running Raspberry Pi OS with the proper country code a bunch prior and everything.
I'm not here just to complain, though. I dug into the issue of the wifi country code that's been giving this build so much trouble. I found a kernel patch and another patch and discussion around our wifi chip which might give an insight - that being, the kernel may be the culprit, or for whatever reason we're not able to write the country code to the NVRAM. There's some related threads on this forum, though I figure they've already been looked over.
Based on that second patch discussion, I tried to manually add ccode=XX (substitute as appropriate and regrev=0 to the NVRAM file brcmfmac43455-sdio.txt, but the first reboot came back with a lot of scary errors (maybe because I rebooted on the command line?) and the second came back with wifi still not working, so I'm unclear if the driver/kernel is even loading the NVRAM files onto the Broadcom chip in the first place. Or if it is, maybe it isn't reading it back?
Might it be worth asking the nexmon team about this, since we're now using their firmware? I found a related issue and a suggested patch that might help re: firmware, though integration into the settings for OpenWrt is another matter. I might test in a bit.