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'm on Fedora Silverblue, which is great now, but when I installed it, I remember thinking that its installer was way less intuitive than Ubuntu's, and I think it also had fewer features (e.g. discovering existing operating systems and offering to install alongside it, IIRC?). I've seen screenshots of a new installer being in development, which looked like an improvement, but still not as smooth an experience as Ubuntu's.