when i boot with usb, no problem, wifi works, one installed, no wifi adapter is found, it's an intel wifi device. I don't understand how come it can work with live usb and no more once installed !!
i found a workaround but updates could remove it, it's not very practical but it works.
sudo apt update
sudo apt install git build-essential
git clone https://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/backport-iwlwifi.git
sed -i 's/CPTCFG_IWLMVM_VENDOR_CMDS=y/# CPTCFG_IWLMVM_VENDOR_CMDS is not set/' .config
sudo make install
sudo modprobe iwlwifi
I solved it by doing
sudo apt-get software-properties-common
sudo add-apt-repository ppa:canonical-hwe-team/backport-iwlwifi sudo apt-get update sudo apt-get install backport-iwlwifi-dkms
sudo apt install linux-generic-hwe-18.04-edge
my wifi card is Intel Wireless AC-9560 - I came across this on another post