The main point of this executive order is likely part of the ongoing issues related to the chevron deference. [1] Chevron deference [1] was a (IMO very weird) legal standard that was overturned in 2024. It required the judicial to completely defer to the executive branch in cases where the laws around executive departments (generally relating to the the limits of their regulatory power/authority) were ambiguous. When this was overturned, the judiciary regained their independence and were once again able to hear and independently judge cases around these executive departments.
This order is now stating that the executive branch departments themselves will no longer be independently interpreting the law at all, but instead defer to the legal opinions of the head of the executive. The order itself also makes it clear that it does not allow rejecting or unreasonably redefining the laws applying to the various departments - instead the main issue is where potential ambiguities and related limits/allowances will be determined. And of course those determinations could then be challenged by either the judiciary or the legislative (by passing overriding laws).
The short version of this is "Executive departments will now be directly accountable to all three branches of government - executive, legislative, and judicial."