Which is the difference betwwen unassign / undeploy a policy from ENTM
This is the Privileged Access Manager section of the PAM Community. Do you refer to some feature of PAM with ENTM, because I am not familiar with that acronym? If you are asking about PAM please clarify your question. If you meant this for another product please post the question in the correct section of the PAM community.
UNDEPLOY basically forces to run the undeployment script on the host which has the policy assigned - yet the policy remains assigned to the host (but finally the deviation calculator might remove the policy after some time - the host might end with policy status UnDeployFailed) - in fact this feature is meant as a troubleshooting mechanisms and should not be used under normal circumstances.
UNASSIGN runs the undeployment script on the host which has the policy assigned - then the policy is removed from the host. - This is the normal procedure to remove a policy from a host.