iPhone not receiving notifications from any app, including WhatsApp

Of course first Off make sure notifications are on in settings. That you can see what notifications are turned on for each app. There is a background setting called “background app refresh”. It should be in “general->background app refresh”. Also check your “focus” settings. Right under “sounds & haptics”, which is under “notifications” in the settings app.

Are you wearing an Watch? That would be normal with an Watch paired.

Ok you will just have to firstly force restart the phone, Force restart iPhone – Apple Support and then check that notifications are on in Settings, Notifications.