How do I use the Password Policy module?
Please see the reference link below which has information about how to use this module for Drupal 8

https://opensenselabs.com/blog/tech/drupal-password-policy-module


There might be other modules like PRLP (Password reset landing
page) or other relevant password setting modules that might not be allowing the policy to be enforced. 
You can check by uninstalling them and see if the created policy is
being enforced on the default user form.