Buttons with no text
WCAG 4.1.2
A button needs a name that says what it does. Icon-only buttons (menu, search, close, cart, slider arrows, quantity plus and minus) are the usual cause.
Screen reader users hear "button" with no idea what will happen. Voice control users can't say "click Search" either.
Give each icon button a short name such as "Open menu", "Search", "Close", or "Next slide". This is usually set in the theme or block settings, or in the code with an aria-label.