GNOME 3.30 Will Bring A Better Flatpak Experience To The Nautilus File Manager
It should be possible to install Nautilus 3.30 on Ubuntu 18.10 as a Flatpak app via the GNOME Repo. This will allow you to use the latest version of the file manager alongside the regular repo version, i.e. without replacing it.
GNOME 3.30 Will Bring a Better Flatpak Experience to the Nautilus File Manager
However, unlike Ubuntu 18.10. Fedora 29 aims to maintain the default Gnome experience. The most visible difference between the two Gnome 3.30-based distributions is the missing support for desktop icons in Fedora 29. This is because desktop icons were never part of the Gnome 3 design goals, and starting with v3.28 the developers decided to axe the six-year-old unmaintained code from the Nautilus file manager.