I don’t think it’s possible with Docker without a reverse proxy, but of course the reverse proxy could run on the same VPS as the Docker containers. Here is an example of what this could look like: Multiple Nextcloud instances on Docker? - #3 by wwe
Another option would be to not use Docker and manually set up a LAMP stack, in which case you wouldn’t need a reverse proxy. You could then simply use multiple VirtualHosts in Apache, each providing a separate DocumentRoot for each Nextcloud instance:
instance1.yourdonain.tld → /var/www/instance1
instance2.yourdomain.tld → /var/www/instance2
etc…