To resolve the "This Device isn't certified by Google Play Protect" issue, please go to Settings > System > Google Device Registration, tap Copy and open the webpage, log in to your Google account on the official website, and then paste the GSF ID to complete the certification.
If tapping Copy and opening the webpage causes a crash, go to Apps, long-press Chrome, enter App info, tap Storage & cache, and Clear cache. After clearing the cache, try the certification process again.