Lol, where? I agree personality wise Horus is annoyingly hung up on Seth just like Osiris, and physically wise Horus does indeed take after Osiris' body shape, but face wise it's like he was Isis and Anubis' love child, lmao (his haircut is almost identical to Anubis', while Osiris seems to be bald if we go by that one flashback where he wasn't wearing his head piece.
There is a close up of his eyes that reminds you of when we are given a close up of Osiris' eyes, but aside from the obvious, Osiris' eyes are darker and we've been shown several times in the flashbacks that Osiris has extremely long eye lashes. Osiris' mouth is also always given lots of more detail: the upper lip being tinted black in most panels, and with a very obvious curve of the medial cleft (aka philtrum, which is the vertical indentation in the middle area of the upper lip). The lower border of his lower lip is also always marked. Horus' lips were not given half of that much detail: his mouth was given a very basic form, in comparison (at least, in this chapter?). That's why I think that aside from the obvious similarity in obsessed attitude, physically wise Horus and Osiris are not that similar, other than about body shape.
His haircut does look like Anubis' prior to Anubis' growth. They both also had that haircut when kids, which is to lend some credence to the fact that Seth would mistake them for each other (yeah... aside from that and Seth's state it not much to go by, I agree, but we all had no choice but to go "whatever you say, author", back then). Even readers who spied the rwas back when the first glimpse of the flashback of child Horus's first encounter with Seth came out, thought it really was Anubis, because of the flashback being black and white confounding the difference in their skin color, and the fact little Horus always with his back to the reader, and they understood that Seth was calling Anubis' name. So yeah... it's far-fetched but there you go, both Seth and the readers mistook them

It’s upsetting how much he looks like Osiris