I note what MITChris explained is similar to what I have seen other AOs explain as well.
It is not that AP scores could never matter to Admissions. And sometimes they matter quite a bit, specifically when there is some specific question or concern Admissions has that a high AP score could address, and the lack of a high AP score will leave unaddressed.
Indeed, not to overrely on anecdotes, but my S24 got a good enough overall score on his first ACT test, but his Math subscore was not quite what it could have been, largely because this was supposed to be just a trial test and he really did not refresh enough on some older math subjects. I asked his very experienced feederish-HS-provided college counselor if this was an issue, and she basically laughed in my face (as politely as she could, but still). She explained because he had gotten a 5 on the BC exam as a junior, and was going to be taking MVC, DiffyQ, and LA as a senior, it was extremely unlikely a college was going to be concerned about his ACT Math subscore.
Anyway, with this context in mind, back to the OP specifically . . . I actually don’t feel like I have enough information from just this thread to fully answer this question. I definitely don’t think a 4 would hurt for US admissions, but I think there are some situations in which it could actually help. Like, if you did not have other advanced science qualifications at all (which I understand can happen in some non-US university prep curriculums), could a 4 in AP Bio, Chem, or Physics help? I think maybe! Same with a math AP if it was your only advanced math qualification, or so on.
As it happens, though, we know from a prior discussion that the OP actually has advanced qualifications for both Math and Chem thanks to their university prep curriculum in Australia. In that context, I am thinking it is unlikely self-study 4s in Stats and Bio are going to be really addressing any important questions. So in this context, I would guess it simply does not matter.