I've not yet seen any indication as to what exactly they have approval to test. My guess is it's literally just something like testing an electrode gel that goes on your skin as part of the process or at most the external parts that interface with the implant. There's an endless world of things the FDA could have given them approval to test as part of their project that doesn't involve actually cracking anyone's skull open and jamming stuff in there to watch them die like the monkeys did. After you get the approval to test your application sponge on real human subject, you launch a press release stating "Neuralink gets FDA approval to move to human testing!" and await that sweet delivious investor money.