I can’t find an example of this used after holding office, only while currently holding office. Didn’t spend too much time looking yet, though.

Other interesting things on the wiki:

“Prior to becoming attorney general in 1991, Deputy Attorney General William P. Barr issued guidance in 1989 about responding to congressional requests for confidential executive branch information. He wrote: "Only when the accommodation process fails to resolve a dispute and a subpoena is issued does it become necessary for the president to consider asserting executive privilege".

Executive privilege is the right of the president of the United States and other members of the executive branch to maintain confidential communications under certain circumstances within the executive branch and to resist some subpoenas and other oversight by the legislative and judicial branches of government in pursuit of particular information or personnel relating to those confidential communications. The right comes into effect when revealing information would impair governmental functions. Neither executive privilege nor the oversight power of Congress is explicitly mentioned in the United States Constitution.[1] However, the Supreme Court of the United States has ruled that executive privilege and congressional oversight each are a consequence of the doctrine of the separation of powers, derived from the supremacy of each branch in its own area of Constitutional activity.[2]

Devolution confirmed with impairing government functions?

Edit: Not a lawyer by any means, but there’s a summary listed on Pogo of what E. P. can/cannot do, and when it applies/does not apply