Under Apache Web server configuration, there’s a prompt to create a symlink to enable the newly created site:

ln -s /etc/apache2/sites-available/nextcloud.conf /etc/apache2/sites-enabled/nextcloud.conf

As the instructions in this section are written for Debian, Ubuntu, and their derivatives, a2ensite should be used instead:

a2ensite nextcloud.conf

The commands are currently functionally equivalent (AFAIK), but should this change sometime, the latter would be more future proof, besides being much shorter and easier to type.

Additionally, immediately following the ln -s there is a section about Additional Apache configurations, which correctly instructs the use of a2enmod to create the symlinks. Replacing ln -s with a2ensitewould thus harmonize the two sections.