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It seems to work if you set rowclass="is-disabled" but that's not particularly helpful if only one of the checkboxes should be disabled. It does mean, however, that the styling works correctly when you disable an entire checkbox row, e.g. via the disabler system.
But indeed there doesn't appear to be a way to mark a specific checkbox as disabled. I'd have expected the disabled attribute to handle it, or at least adding class="is-disabled" to the option.
IIRC, we intentionally split up separating the disabled styling from the disabled attribute to give more flexibility, though it was likely more in the context of buttons. It may be clearer to drop that, or at least do it via [disabled]:not(.some--modifier).
That said, I think there may be a specific regression here from the checkbox/radio replacement.