hey again, alright let's give these steps a go, hopefully we can do it the simple way!!
1.Open WhatsApp and go to Settings > Notifications and make sure the notification preferences are turned on.
2.Check the Do Not Disturb settings. These can affect the kind of app notifications you receive, how notifications show up, and when you get one. Double-check to make sure this feature isn't making your WhatsApp notifications silent.
3. try backing up all WhatsApp data manually through the settings in the app, then go to Settings, apps, WhatsApp and clear data and cache then run the app and restore back up and test again.
4. Update the WhatsApp app, sometimes apps needs checking for updates manually but could still work without somewhat. Via PlayStore.
5.Check if Low Power Mode is turned on. Many devices have a feature that automatically deactivates background app activity and notifications when the battery power runs low. Check to make sure this wasn't activated accidentally.
6. Unstable WhatsApp, (you still have your backup) reboot your device and reinstall!
let's try these first, and continue if this doesn't fix it