As u can see it says pop-up notifications are no longer available for your version of Android help me about this fix this issue asus
Looking into it, if you see on Web its something related to Android and What's App.
This is not specific to ROG Phone 3. All android 10 phones (including OnePlus, Samsung, Huawei, Oppo, Xiaomi, Vivo) has this problem. Until Whatsapp comes up with a fix, there is nothing you can do.