Where is the apache conf and how restart apache?
   Where is the php.conf and how restart php service?
   Where is the nextcloud conf and how restart nextcloud?
   Where is the www root folder to add some other html/php files?


   /snap/nextcoud/current/conf/httpd.conf.
   You can restart the Apache server using snapd's tooling:
   sudo snap restart nextcloud.apache
   /snap/nextcloud/current/config/php/php.ini
   There isn’t a php daemon as such in this configuration - looks like it is run per-request, so you wouldn’t even need to restart Apache to apply any changes. Just reload/refresh the page.
   /snap/nextcloud/current/htdocs/config/config.php
   Nextcloud doesn’t have a daemon at all, it’s all just php. See above.
   /snap/nextcloud/current/htdocs/