Taken from: https://serversforhackers.com/c/nginx-php-in-subdirectory

nginx-location-subpath-with-php.conf

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    root /var/www/top/public;

    index index.html index.htm index.php;

    server_name _;

    location / {
        try_files $uri $uri/ /index.php$is_args$args;
    }

    location /nested {
        alias /var/www/nested/public;
        try_files $uri $uri/ @nested;

        location ~ \.php$ {
            include snippets/fastcgi-php.conf;
            fastcgi_param SCRIPT_FILENAME $request_filename;
            fastcgi_pass unix:/var/run/php/php7.2-fpm.sock;
        }
    }

    location @nested {
        rewrite /nested/(.*)$ /nested/index.php?/$1 last;
    }

    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/var/run/php/php7.2-fpm.sock;
    }
}