After reading more about it, it seems that when a policy is considered to be a factor and not under the control of the project team, then it is considered an EEF.
Moreover, a hiring policy is actually a factor that may be positive or negative affect on the project.
If someone can, please confirm if this the above is correct and also provide more examples of policies that are actually considered to be an EEF

Can someone please clarify why "human resource management policies regarding hiring termination..." are considered EEF on the Develop team input section 9.4.1.3?

Until now my understanding was that policies and procedures are OPAs.