The UI or DE (desktop environment) is actually interchangeable no matter what diatro you’re on. But KDE is kind of moving ahead as the favorite it seems. The you have Gnome, which is what vanilla Ubuntu comes with… And that has spinoffs like cinnamon that come with Mint.
A few distros have really made the user experience pretty damn simple. I personally love EndeavourOS as it seems to be the best of all worlds for me personally. But for any of my non techy friends, I suggest or personally set them up with Mint more often than not Mint is a far better experience overall than Ubuntu in my opinion. But I greatly prefer the package manager (yay) in EndeavourOS.