A focused control must not be hidden behind a sticky header, cookie banner, or chat widget. WCAG 2.2 added this as a separate criterion because a perfect focus ring is worthless if something is sitting on top of it.
WCAG 2.4.11 — Focus Not Obscured (Minimum) (Level AA)
WCAG 2.4.12 — Focus Not Obscured (Enhanced) (Level AAA)