How to install Nextcloud 13 on Ubuntu 18.04

Now there's a much simpler way to install the latest version of NextCloud onto your Debian-based server as follows.
"snapd" is not included in the debian installation, but it can be easily added via "apt install snapd" as root. Once that's done, go ahead as in Ubuntu and "snap install nextcloud", wait for the installation to do its thing and voilà!