When attempting to delete a policy, the console returns the error "Unable to delete policy as it is either assigned to asset group or is a part of policy group"
On the policy screen, it shows that it is not assigned to any groups.
An earlier version of the policy is still assigned to a group. The status on this screen only reflects the assignment state of the latest policy version.
Review earlier versions of the policy from the Policy Details > Policy Version tab to find which version of the policy is still assigned, and unassign it from there.
Once this is done, the policy should be deletable.