Hi kiddokate13,
Welcome to Apple Support Communities. We understand that your iPhone 12 Pro is making notification sounds but there is no visible notification.
Does this sound like a notification sound that you have set for a certain app? Check to see if any of your apps notification settings have only Sounds turned on. You can do that by going to Settings > Notifications, then scrolling through your apps. If you see any that are Sounds only, try turning on banners or badges to see if that helps identify the app notification. Check out Use notifications on your iPhone, iPad, and iPod touch as a reference if needed.
Take care.