I think I found a solution for apps like WhatsApp, Facebook messenger , gmail and YouTube I wasn’t getting notifications for these and I have tried uninstalling and installing on 14.2 but It didn’t work then but seems to be working on 14.3.
Before doing it for the apps like WhatsApp Try it on Gmail or Facebook cause they don’t need a backup
You have to do perform the following steps
Number one uninstall the app that is having the problem
Turn off the phone
Turn on the phone and install the app again ,it will ask for the permission for notifications select allow notifications
Since my backup for WhatsApp was larger than 5 GB I subscribed to the trial version of Apple one which gave me 50 gigs of iCloud storage and I backed up WhatsApp on it and a other apps which were having the problem and then one by one I reinstalled them
Now all of them are working properly.
The solution works for 14.3 I don’t know about the previous versions
Hope it works for you