Is it possible to anonymously leave online reviews for businesses?

If that’s the case, then you need privacy. Not anonymity. It’s unnecessary to go overboard without cause. If you need a Google account or whatnot, you can always make one with different name even though you may need to verify your number. And then use that account for all your pseudonymous needs. In this case, only Google may infer that it’s your account even if you’re using a different name.