I've just installed the mongodb extension with PIE on a new Deian 13 server, and it puts the 80-mongodb.ini file in /etc/php/8.4/cli/conf.d/ only.
Instead, it should have created /etc/php/8.4/mods-available (as mongodb.ini) and then link it into /etc/php/8.4/cli/conf.d and /etc/php/8.4/fpm/conf.d as 80-mongodb.ini.