You can always download the full-install from Nextcloud and unzip it somewhere. Then just copy the .htaccess and .user.ini from that unzipped install into your actual install. As I said, since these two are to be supposed to be as shipped, they need to be always the same.
As far as the php settings for an NginX install goes… I had to struggle myself a bit with that and since we’re also using php-fpm, things seemed even more unclear at first, but in the end it’s pretty easy: you will have to adjust the php settings in /etc/php.ini, e.g. the memory size and probably the size for the max. upload size.