For example, I’m using Debian, and I think we could learn a thing or two from Mint about how to make it “friendlier” for new users. I often see Mint recommended to new users, but rarely Debian, which has a goal to be “the universal operating system”.
I also think we could learn website design from… looks at notes …everyone else.
I usually use Fedora these days and I have few complaints but I sometimes miss the ArchWiki. Not that Federa isn’t well-documented — it obviously is well documented by nature of being a RedHat product — but people in the Arch community will sometimes make a whole page to document how they fixed a specific laptop model’s relatively unimportant hardware compatibility issue.
I’m on Fedora too and quite often end up on the Arch wiki. A lot of the stuff there applies on other distros too.