Keyboard operability (keyboard-operability)
All interactive elements (e.g., buttons, links, forms, and menus) are accessible and usable via keyboard input alone.
Tabindex="-1" on iframe:
This <iframe> contains a visible "Home" link, but using <tabindex="-1"> removes it from keyboard navigation. As a result, keyboard users cannot access the link, which fails WCAG 2.1.1.