I had exactly the same problem, and I was trying to solve it for 2 days, in addition to setting trials I restored my device several times, but none of them solved the problem. I find a neat solution from Apple forums. I tried it and solved my problem.
https://discussions.apple.com/thread/250814508
- Download WhatsApp Business.
- Port your account over to WA Business (click continue after opening the app) without deleting the normal WhatsApp.
- Try to get someone to test send a few messages to your number. WA Business should push out the notifications.
- Delete your normal WhatsApp and restart your iPhone.
- Re-download and reinstall the normal WhatsApp from the App Store. Open the app and allow porting of info to take place.
- And there! Notifications should come in as per normal again on your normal WhatsApp!!!
- Delete the WA Business app if you have no use for it.