Source list
vim /etc/apt/sources.list
deb http://deb.debian.org/debian buster main contrib non-free deb-src http://deb.debian.org/debian buster main contrib non-free deb http://deb.debian.org/debian-security/ buster/updates main contrib non-free deb-src http://deb.debian.org/debian-security/ buster/updates main contrib non-free deb http://deb.debian.org/debian buster-updates main contrib non-free deb-src http://deb.debian.org/debian buster-updates main contrib non-free deb http://deb.debian.org/debian buster-backports main contrib non-free deb-src http://deb.debian.org/debian buster-backports main contrib non-free
Install Intel 9260 wireless
apt-get update apt-get install firmware-iwlwifi modprobe -r iwlwifi ; modprobe iwlwifi