Ok, if I’m understanding your situation, you have a non-snap Apache server already installed and serving some other web root, and what you need is a named virtual host added to your Apache server that will reverse proxy traffic to Nextcloud.
A named vhost allows Apache to deliver a different site based on the URL that was used, even though it’s ultimately coming to the same IP and server.
I have such a setup in my guide for installing Nextcloud with Docker. The Apache virtual host configuration to reverse proxy for snap should be pretty similar.