No wlan interfaces found on CM4 after firmware update

The first image that appears to have displayed this was from 20210115

Also happens on 20.04 armhf released image after dist-upgrade everything with proposed repository enabled.

Image:
ubuntu-20.04.1-preinstalled-server-armhf+raspi.img.xz

This should be fixed in the 3-0ubuntu2 release. This has been released in hirsute, and should now be in -proposed for focal.

Using ubuntu mate on rpi 4b. Faced this same issue today when I upgraded the package.

Selecting previously unselected package linux-firmware-raspi2.
Preparing to unpack .../63-linux-firmware-raspi2_4-0ubuntu0~20.04.1_arm64.deb ...
dpkg-divert: error: 'diversion of /lib/firmware/brcm/brcmfmac43455-sdio.bin to /lib/firmware/brcm/brcmfmac43455-sdio.bin.distrib by linux-firmware-raspi2' clashes with 'diversion of /lib/firmware/brcm/brcmfmac43455-sdio.bin to /lib/firmware/brcm/brcmfmac43455-sdio.bin.distrib by pi-bluetooth'
dpkg: error processing archive /tmp/apt-dpkg-install-8lVGqH/63-linux-firmware-raspi2_4-0ubuntu0~20.04.1_arm64.deb (--unpack):
 new linux-firmware-raspi2 package pre-installation script subprocess returned error exit status 2
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43430-sdio.clm_blob by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43455-sdio.raspberrypi,4-compute-module.txt by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43455-sdio.raspberrypi,400.txt by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43436-sdio.bin by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43436-sdio.clm_blob by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43436-sdio.txt by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43455-sdio.clm_blob by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43456-sdio.bin by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43456-sdio.clm_blob by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43456-sdio.raspberrypi,4-model-b.txt by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43456-sdio.raspberrypi,4-compute-module.txt by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43456-sdio.raspberrypi,400.txt by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43430-sdio.bin by linux-firmware-raspi2', none removed.
No diversion 'diversion of /lib/firmware/brcm/brcmfmac43430-sdio.raspberrypi,3-model-b.txt by linux-firmware-raspi2', none removed.
dpkg-divert: error: mismatch on package
  when removing 'diversion of /lib/firmware/brcm/brcmfmac43455-sdio.bin by linux-firmware-raspi2'
  found 'diversion of /lib/firmware/brcm/brcmfmac43455-sdio.bin to /lib/firmware/brcm/brcmfmac43455-sdio.bin.distrib by pi-bluetooth'
dpkg: error while cleaning up:
 new linux-firmware-raspi2 package post-removal script subprocess returned error exit status 2
Preparing to unpack .../64-linux-libc-dev_5.4.0-73.82_arm64.deb ...
Unpacking linux-libc-dev:arm64 (5.4.0-73.82) over (5.4.0-72.80) ...
Preparing to unpack .../65-openvpn_2.4.7-1ubuntu2.20.04.2_arm64.deb ...
Unpacking openvpn (2.4.7-1ubuntu2.20.04.2) over (2.4.7-1ubuntu2) ...
Preparing to unpack .../66-pi-bluetooth_0.1.15ubuntu0~20.04.1_arm64.deb ...
Unpa...

Your problem is the upgrade of pi-bluetooth:
Unpacking pi-bluetooth (0.1.15ubuntu0~20.04.1) over (0.1.10ubuntu6-lobo) ...

0.1.10ubuntu6-lobo is not an official Ubuntu package version. Where did it come from? It seems to add some diversions that are incompatible with the new version 0.1.15ubuntu0~20.04.1.

This bug is fixed in the current version of focal:

ubuntu@ubuntu:~$
ubuntu@ubuntu:~$ apt-cache policy linux-firmware-raspi2
linux-firmware-raspi2:
  Installed: 4-0ubuntu0~20.04.1
  Candidate: 4-0ubuntu0~20.04.1
  Version table:
 *** 4-0ubuntu0~20.04.1 500
        500 http://ports.ubuntu.com/ubuntu-ports focal-updates/multiverse armhf Packages
        100 /var/lib/dpkg/status
     1.20200212-0ubuntu1 500
        500 http://ports.ubuntu.com/ubuntu-ports focal/multiverse armhf Packages
ubuntu@ubuntu:~$ cat /proc/device-tree/model; echo
Raspberry Pi Compute Module 4 Rev 1.0
ubuntu@ubuntu:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether dc:a6:32:fe:ba:b0 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.56/24 brd 192.168.0.255 scope global dynamic eth0
       valid_lft 42801sec preferred_lft 42801sec
    inet6 fe80::dea6:32ff:fefe:bab0/64 scope link
       valid_lft forever preferred_lft forever
3: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether dc:a6:32:fe:ba:b1 brd ff:ff:ff:ff:ff:ff
ubuntu@ubuntu:~$