I think that something specifically intended for this, like Anubis, is a much better option.
Not sure if that's the intended use case. At least Cloudflare politely masks for CAPTCHA.
Are you sure the block isn't due to the authors of those websites using some other tool in addition?
Imagine Cloudflare "You're blocked" page, but with different design and logos.
I don't think it requested anything else, at least I didn't see anything else. If I find this page again, I'll reply with a link to the screenshot.