Here in Massachusetts, the state legislative branch had been audited by a outside, 3rd party, but recently, by referendum, the state legislative branch will now be audited by the executive branch - which understandably brought up the argument that state executive branch auditing the state legislative branch violates the separation of powers described in the Massachusetts Constitution. I do think we need to have every branch of federal government audited, tested, scrutinized by (hopefully) disinterested 3rd parties.
Tax season has many people diligently filing their returns to avoid being audited. While the federal government is not a tax-paying entity, it actually undergoes an audit of its financial statements every year. How do we know? Because we perform the audit!
www.gao.gov
However, the POTUS just dragging in someone, apparently anyone they so choose, to do the auditing of the executive branch, is just nuts. What if, instead of Elon Musk, Trump, by virtue of being given a 'mandate from the people', decided to bring in some random buddy of his to audit the executive branch? Say Rudy Guiliani? According to you and Trumpists, this is okay, because, well he's President and you're not.