I\'ve just recently moved my websites from apache2 to Nginx as my new web server backend. got to love problems aha.
HTML files in the web host director work prior to php
Check your php7.x-fpm.sock file to see what version they are.
php7.x-fpm.sock
Mine was: php7.0-fpm.sock instead of php7.2-fpm.sock
php7.0-fpm.sock
php7.2-fpm.sock
Don't forget to also change its name in /etc/nginx/site-enable/example.com
/etc/nginx/site-enable/example.com