The Clear focus guideline asks for :focus-visible so a focus ring shows up for keyboard users and stays out of the way for pointer users. The next sentence then recommends :focus-within for grouped controls, which follows a different signal.
:focus-within matches an element when that element or one of its descendants matches :focus. Selectors Level 4 defines it that way, and MDN restates it: the pseudo-class represents an element matched by :focus, or an element with a descendant matched by :focus. A group styled with :focus-within still highlights when a child is focused with a pointer.
:has(:focus-visible) is the group equivalent of :focus-visible. The group matches only when a descendant's focus indicator should be shown, so compound controls follow the same rule as the focused element itself. Both :has() and :focus-visible are Baseline widely available.
The wording is updated in the guideline, the review command, and the agent rules.