If the succeeding president can revoke the executive privilege of his predecessors, then there is no such thing as presidential privilege. This is the biggest constitutional crisis in the history of the country.
We know that it ex post facto laws punishing acts that are not illegal in the past are unconstitutional. What about ex post facto nullification of a former president's executive powers?
The Biden/Obama gang has already used the DOJ/FBI to act as if we lived in a temporary banana republic. If they don't back down from political pressure, or the courts allow Biden to nullify Trump's executive privilege, we could have a permanent banana republic.