They shouldn’t have called it a “challenge” there. It’s not a challenge; it’s just executing the verification function. Chalk up another one for harmfully incorrect terminology. (Admittedly “verification” is also an overloaded term, as it gives you a token which your backend subsequently needs to verify.)

(As they confirm near the start of the document, “reCAPTCHA v3 will never interrupt your users, so you can run it whenever you like without affecting conversion.”)