Per Google policy, each client must be signed into their Google account in order to leave a review. 75% of people are logged in via Youtube, Gmail, or Google Drive. If they are not logged in, they are first presented with a sign-in screen. This is how Google tracks who is leaving a review, this stops an angry customer burying you with 100 bad reviews while also stopping the store owner from leaving 100 good reviews. Google needs to know who is leaving the review. There is no way around this. Here is a helpful article with more reasons https://taptag.shop/blogs/news/is-there-a-way-for-users-to-not-have-to-sign-into-google-to-leave-a-review