No. This button is completely uninformative and enables only proprietary but free stuff like Chrome, Jetbrains, Steam and NVidia drivers.
It does not
enable flathub
enable rpmfusion
I use Fedora and I know what I am talking about. The KDE people are currently adding the same "add external repos" button to the Plasma welcome screen, at least something.
But you still have
"flatpak apps" but from the wrong source and sometimes broken (just imagine how confusing this is for new users. Having "the flatpak alternative" but its also wrong.)