Clicking on WEB INSTALLER opens an accordion, and there is a bullet point " * Right-click here and save the file to your computer" but there is nothing to click there…
There seems to be nothing to click and the link to the admin documentation does not help.
A hyperlink directly to the web installer is needed.
Web Installer
The Web Installer is the easiest way to install Nextcloud on a web space. It checks the dependencies, downloads Nextcloud from the official server, unpacks it with the right permissions and the right user account. Finally, you will be redirected to the Nextcloud installer.
Right-click here and save the file to your computer
Upload setup-nextcloud.php to your web space
Point your web browser to setup-nextcloud.php on your webspace
Follow the instructions and configure Nextcloud
Login to your newly created Nextcloud instance!
You can find further instructions in the Nextcloud Admin Manual.
Note:
Installer uses the same Nextcloud version as available for the built in updater in Nextcloud. After a major release it can take up to a month before it becomes available through the web installer and the updater. This is done to spread the deployment of new major releases out over time.
I do not recommend using the web installer. Nextcloud is not very suitable to run on a web space. This will lead to trouble sooner or later. Can you post details to your Nextcloud instance? Perhaps you can better use a Managed Nextcloud (from e.g. another hoster). You can get it for free (single user instance).