You can't split the web directory from the rest of the installation.
The installation guideance lists the sensible options. You'll need to contact your web host to see if you can add an alias, in which case, you'd put all the Xibo files outside of public_html, and alias say
/xibo to wherever you've put those files - eg
Alternatively, you may be able to create a symbolic link, in which case, you'd make a symlink from
/public_html/xibo to wherever you've put the Xibo install, in to the web directory - eg
Both those routes will require you to edit the
.htaccess file we ship to add /xibo in to the URL rewriting schema.
We have never recommended running Xibo on shared hosting. It has always been at odds with that kind of environment, and so it might be time to look at moving to something more flexible like a VPS, or something that can run Docker containers, or to specific Xibo hosting.