I haven't tried on macos, but yeah, the biggest problem right now seems to be implementation differences with how embedded spaces are handled. Earlier, the biggest cross-browser issues were pixel alignments within the QR codes, but those seem largely resolved.
The page says that “browsers may split a QR code across lines” - but this isn’t split across lines.
Experimenting, if I just type "[Q R]" (very short, so not likely to line-break), the problem still occurs.
If I inspect the element, and add `white-space: nowrap;` to its style, the problem still occurs (although the text doesn’t wrap!).