Ubuntu 18.04 cannot recognized Intel Wireless-AC 9260

It is a problem with fast startup mode of Windows. I think because in that mode, Windows keeps the wireless adapter for itself when shut down. hence Linux cannot detect it.

Just go into Settings > Power & Sleep > Choose what power button does > Shut down setting > uncheck the Turn on fast startup > save change and it will work.

iwlwifi-9260-th-b0-jf-b0-34.ucode is included in the package linux-firmware in Ubuntu Bionic.

Try upgrading or reinstalling the package.

apt-get --reinstall install linux-firmware

Don't try to manually install from an archive provided by Intel. Always try to find a package that provides the driver if possible.

The Intel 9260-AC Wireless Chipset doesn't work in newer Linux kernels (ex: Ubuntu 18.04).

Here is the kernel bugreport that can be checked for the status.

In my case this was affecting a freshly bought: Lenovo IdeaPad/Yoga S730.

The solution for me was to install Ubuntu 16.04 with an older kernel, which worked without any issue

Edit 2021-01-18

The wireless adapter in the IdeaPad/Yoga S730 is working fine on ubuntu 20.04