> GAO is a Congressional agency, it does not fall under the Executive
I don't know that it's accurate to say such things any more, due to the unitary executive decree by the supreme council. The GAO is intrinsically motivated by law - both to carry out its purpose, and simply to pay its employees - and the supreme council has decreed that all execution of the law is subject to the whims of the president. If the president woke up from his afternoon nap and told GAO employees they weren't going to get paid unless they did a certain thing, it's certainly possible that the supreme council might walk back their earlier decree (although good luck with the payment infrastructure already being pwnt and all that). But it's also possible they might not, given how they've already approved other autocratic dynamics.
They aren't part of the executive branch, period. The president has no control over their pay or performance. Hell, the president doesn't have nearly as much control over the executive branch as you imply, however much he might want it.