Ubuntu 20.04 LTS on DELL laptop - no wireless internet connection

I'm new to Linux and I recently installed Ubuntu 20.04 LTS on my old laptop: DELL XPS-15 L501X. The internet connection by cable works fine. I can connect my laptop wireless to the router but in this case I get no internet.

My network controller is: Intel Centrino Advanced-N 6200

More information (from wireless-info script) here: https://paste.ubuntu.com/p/m7MNkwChMJ/

Until now I've seen on this webpage: https://wireless.wiki.kernel.org/en/users/drivers/iwlwifi that the driver for my network controller is in a file called:

iwlwifi-6000-4.ucode

then I downloaded this file in it's most recent version from: https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git

I copied it to the directory /lib/firmware on my laptop and rebooted it.

My wireless internet connection is still not working. Any idea ?

Finally got wireless internet. After trying a lot of solutions and no one worked for me, I found on this forum: https://forums.linuxmint.com/viewtopic.php?t=161876 the following four commands:

echo "options iwlwifi 11n_disable=1" | sudo tee -a /etc/modprobe.d/iwlwifi.conf
sudo modprobe -rfv iwldvm
sudo modprobe -rfv iwlwifi
sudo modprobe -v iwlwifi

and now wireless internet is working on my laptop although I got some error messages after executing the third command.

The original explanation of the code (from the above forum), is here:

"The first line puts a line of code inside to iwlwifi.conf file. The next two lines unloads the iwldm and iwlwifi and the last one reloads it. If these don't work just delete the added line from the file and do the last three again. Finally, just write down the code to somewhere safe cause some kernel updates (not all) wants it to be done again, last three one are enough if it stops working."

I hope this answer will save time for others.