I don’t think you need to do all this development. There should be no need to create own files. Basically, it is quite simple.
- adjust
/etc/nginx/sites-available/defaultand changeroot /var/wwwintoroot /var/www/nextcloud - adjust
/etc/nginx/sites-available/defaultand remove small block forlocation / - adjust
/etc/nginx/sites-dietpi/dietpi-dav_redirect.confand remove sub path/nextcloudfrom all configs - adjust
/etc/nginx/sites-dietpi/dietpi-nextcloud.confand remove sub path/nextcloudfrom all configs (should be quite some) - restart Nginx