The main difference between Ubuntu and Fedora is the package manager. Most of the rest is just selected default values for configuration and cosmetics, and what helper scripts are or aren’t present on the system. They’re both mainstream distributions aimed at the general user, and they’re shaped by their goals.
To see how different distributions can be, you need to compare the mainstream distributions to stuff that’s decidedly not mainstream, like Gentoo, Alpine, and Nix.
Just as a trivia note: Gentoo does package a couple of other distros’ package managers (app-arch/rpm and app-arch/dpkg), for use in installing otherwise-unavailable commercial binaries, although I suspect app-arch/rpm2targz sees more use than either of them.