While everybody's right in saying text captchas are outdated, there are concerning amount of services (especially for small-mid businesses) that still use them.

Anyway, if an AI could control something like Selenium with the necessary modifications (aka not presenting itself as Selenium), I am pretty sure most of the "Click here to confirm you are an human" captchas like the cloudflare one would be defeated too.

I think the most challenging are image-based weird challenges that are difficult even to humans. The annoying ones.