I spent most of the day yesterday looking into this issue. I found that there were 3 packages installing duplicate firmware and they all seem to be out of date. linux-firmware is now installing the wifi firmware for one example. I have downloaded what that is the latest wifi/bluetooth from the RPi people. Between me and @strit which his pi 400 came in today his wifi and bluetooth seems to be working now.
Try this:
When done you will have no firmware on the system except the
latest firmware from the Rpi people. They will be the exact
files that will be in the Pi OS image.
# Backup in case you want to restore:
Rename /usr/lib/firmware/BCM4345C0.hcd
Backup /usr/lib/firmware/brcm directory
Backup /usr/lib/firmware/updates/brcm directory
Clear out the files in /usr/lib/firmware/brcm directory
Clear out the files in /usr/lib/firmware/updates/brcm directory
# Copy over the new firmware from the tarball below:
Put the new wifi firmware in /usr/lib/firmware/brcm directory
Put the new bluetooth firmware in /usr/lib/firmware/updates/brcm directory
The tarball has 2 folders in it (pi-bluetooth and wifi) with the latest firmware.
https://drive.google.com/file/d/1L_2mZKLDkwaJp7p86go6iNkkAj9Re9Mz/view?usp=sharing
When done reboot the pi 400