What about clicking a checkbox means I'm human? How does Cloudflare determine I'm human from that?
The simplicity of it is logic defying. It used to be that you had to find crosswalks or move puzzle pieces or type blurred letters and numbers, but NOW all the sudden I can just click a box and HEY!, I'm human?
These type of “captchas” look at your browsing behavior. It is sort of a “trade secret” of what it looks for, but it might be screen resolution, mouse behavior, cookies, OS, time to click, etc. Anything a website has access to that would look different from a bot.