Ubuntu’s popularity means that it’s the best supported desktop Linux out there. We don’t have room to list all the official forms of documentation and tutorials on the website, while tutorials on the web often assume you are using Ubuntu. The official forum is split into different subforums and it’s fairly busy, meaning that nearly all questions receive a reply. Linux Mint is also an extremely popular distribution and benefits from the fact that it has a shared infrastructure with Ubuntu and Debian. Nine times out of ten, you can fix a Linux Mint problem or figure out how to do something by simply following the instructions that would work under Ubuntu.
Occasionally, there are differences, but Linux Mint has a big enough community to carry it.
Linux Lite is derived from Ubuntu, meaning a lot of solutions for that distribution work here, too. The site is marred by the prevalence of adverts, but contains a set of well-illustrated articles specifically relating to Linux Lite and a forum that has a healthy level of traffic.
The Pop!_OS website surprised us with how extensive its collection of short articles and videos that focus on the unique aspects of the distribution is. The focus is on areas in which Pop!_OS is different from its parent distribution, Ubuntu, which makes sense.
MX Linux has Mepis, Debian and antiX roots, and it features some good home-grown tutorials and videos on the website, and a forum with a healthy level of traffic. However, tracking down information might be overwhelming for people who are less familiar with Linux.