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That doesn't mean it's worth using.

Agreed, it's morphed into something a lot more evil than stopping bots. The amount of heuristics it now collects in v3 is quite something. Check for your score yourself https://recaptcha-demo.appspot.com/recaptcha-v3-request-scor...

> This is a sample implementation, the score returned here is not a reflection on your Google account or type of traffic.

I got 0.9 and then 0.3 after refreshing.

That's by design. Hitting the same endpoints multiple times is botty behaviour. I got 0.9 three times, then 0.7 on the fourth.

What's your solution against a dedicated attacker?

To be attacked.