hi bro, do perform “settings - general - reset - reset all settings” once. then make sure all apps are updated to latest version. avoid using low power mode temporarily.
Also perform “settings - general - reset - reset location and privacy settings” once.
When you open whatsapp next time after this reset, it will ask for notification allow permission. Give allow and continue using it for 2 to 3 days. see how it works after this.