What do you mean? It doesn't matter how many popups or CAPTCHAs the sites make you deal with: as long as you don't log in to your Google account, any searches you make with an incognito window shouldn't be associated with your Google identity. They'll be associated with your IP address (and of course browsers can in principle be fingerprinted, etc.)
If there's any reason to believe that Google tries to defeat incognito mode and associate that history with a particular Google account, I haven't heard it, and it seems really unlikely, given the things people are expected rely on incognito mode for.
If there's any reason to believe that Google tries to defeat incognito mode and associate that history with a particular Google account, I haven't heard it, and it seems really unlikely, given the things people are expected rely on incognito mode for.