Comment 29 for bug 1848953

sudo apt purge backport-iwlwifi-dkms
Package 'backport-iwlwifi-dkms' is not installed, so not removed

dkms status
(shows nothing)

5.4.0-050400rc6-generic #201911031940 SMP Mon Nov 4 00:43:05 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Restarted system and tried to join both wifi frequencies; only 5 GHz works.
dmesg for kernel 5.4 log attached. I will be back with kernel 5.6.

I also just installed and tried the latest mainline kernel, v5.6 (https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.6/):
-rw-r--r-- 1 florin florin 11127504 apr 4 23:17 linux-headers-5.6.0-050600_5.6.0-050600.202003292333_all.deb
-rw-r--r-- 1 florin florin 1180920 apr 4 23:18 linux-headers-5.6.0-050600-generic_5.6.0-050600.202003292333_amd64.deb
-rw-r--r-- 1 florin florin 9053444 apr 4 23:19 linux-image-unsigned-5.6.0-050600-generic_5.6.0-050600.202003292333_amd64.deb
-rw-r--r-- 1 florin florin 52319388 apr 4 23:19 linux-modules-5.6.0-050600-generic_5.6.0-050600.202003292333_amd64.deb
sudo dpkg -i *.deb

With kernel v5.6 no wifi connection works.