Apple Watch's OLED seems great with even the densest QR code profiles. (I have an older Series 5, I think, and have never had a problem scanning a QR code from the watch.) I think Apple tests it heavily, too, because a lot of the codes on "Apple Wallet cards" for things like a store's rewards program get scanned as QR codes, and at least several of those are extremely dense. (I haven't done the debugging myself, but I believe I read on HN elsewhere that at least one was just stuffing a full bloated JWT into a QR to explain its extreme density.)