This short tutorial for Apache 2.2 worked:

https://www.kutukupret.com/2016/06/29/centos-6-httpd-2-2-and-php-fpm/

Actually, the following should have worked too, there’s no mention for the need of installing fastcgi at all, I assumed php-fpm by itself would be enough but that doesn’t seem to be the case. Maybe an Apache 2.4 thing?

https://developers.redhat.com/blog/2017/10/25/php-configuration-tips/