Unfortunately there’s still no Files snap and there’s nothing about that listed here so I wonder if it’s not going to happen soon. @kenvandine?
There won’t be a stable Files Flatpak for a while either:
Nautilus is improving Flatpak integration before delivering it as stable, in the meantime the maintainers encourage you to test the development version from https://sdk.gnome.org/gnome-apps-nightly.flatpakrepo
To get the development version get Flatpak with
sudo apt install flatpak then just download this, open a Terminal in the folder you downloaded it to and run
flatpak install nautilus.flatpakref. Please note that it is very buggy (and the developers know that it’s very buggy so don’t file bugs about it), currently I’m not able to open any files with it!
See my previous post for more, everything I said there still applies, Files 3.28 is in Debian Experimental and you can grab it from there (though you may break your system in the process and you’ll get no automatic updates) but it’s not in Debian Unstable or Testing yet.
I’m afraid everyone needs to be really patient, you won’t be able to get Files 3.28 in a safe and working manner (on Ubuntu, at least) until there’s a Files 3.28 snap (which doesn’t seem to be on the horizon), a stable Files 3.28 Flatpak (which doesn’t seem to be on the horizon either really), or Ubuntu 18.10 is out.