This rewrites the selector to use :has() because .form-floating is a parent container, which has no :disabled state. The :disabled is handled on the individual form element.
That said, it'd be really cool if adding a disabled attribute on a parent element would disabled all the elements within—right now only fieldsets do that. And I genuinely just stumbled back into thinking about this... so what if we used fieldsets here in v6? Something to think about.
Anyway, the downside of using the :has() selector is browser compatibility right now. I'm not super worried about that as this could be seen as a progressive enhancement, but it's worth calling out. With the new selector, nothing is generated for disabled fields, so we avoid that problem entirely.