It is actually possible to style a <dialog> with a pure CSS fallback for reveal, e.g such that it also appears via :focus-within activated using a <label> that targets a nested but invisible input, which is feasible even if JS is disabled or locally malfunctioning. I’ve made this construction work but it is obviously a hack, and rather page-specific so we didn’t turn it into a library component. The result also had accessibility issues, which we did fix with JS, rationalised on the basis that ARIA by definition means JS availability.

Personally I’d rather that the toggle was available as an activation behaviour, and this is an open issue for the HTML standard. https://github.com/whatwg/html/issues/3567