Slow WiFi on Manjaro Default Image 20.04 for PBP

[nekojet]

Thanks for the dmesg suggestion.  It seems like the firmware is only a few months old:
[   10.038083] brcmfmac: brcmf_c_preinit_dcmds: Firmware: BCM4345/9 wl0: Feb 11 2020 11:54:51 version 7.45.96.61 (be7af2d@shgit) (r745790) FWID 01-a41d86bd es7.c5.n4.a3

And from inxi -F, the wireless adapter chipset does not even show:
Network:   Message: No ARM data found for this feature.
          IF-ID-1: docker0 state: down mac: 02:42:b9:43:98:13
          IF-ID-2: wlan0 state: up mac: c0:84:7d:25:39:fa

And Package Manager shows: ap6256-firmware 2020.02-1 (for the ap6256 wifi/bt module) was installed.

I'm running the same configuration. When I initially installed 20.04 to the eMMC, Wi-Fi worked on both 2.4 GHz and 5 GHz. I didn't test the speed because the first thing I did was an update (sudo pacman -Syu). After the update, it stopped displaying the 5 GHz connection as an option (so that's a slightly different result). 2.4 GHz works fine.

So I'm having that hiccup. If everything worked perfectly I'd never learn anything, so it's all good.

[UPDATE: 2020.05.30]

I started from scratch with the Manjaro ARM 20.04 image, verified that my 5 GHz connection was working (and speedy), configured Pacman to ignore:

ap6256-firmware

then did the full upgrade (sudo pacman -Syu).  This left:

ap6256-firmware 2020.01-1

in place, instead of upgrading to:

ap6256-firmware 2020.02-1

After the upgrade completed, I retained full 5 GHz Wi-Fi functionality (and speed).  Thanks for the clues!

Cheers!