Notifications not working for multiple apps

I have an iPhone XS Max that I got in January of 2019. It's worked perfectly until a month or two ago, when I realized I wasn't receiving notifications from several apps, including WhatsApp, Snapchat, Goodreads, Discord, and Instagram. All apps were fully updated and all notifications were turned on within the app and globally on the phone. I have updated to iOS 15.3, the apps are still fully updated, I have restarted my phone - I have tried everything. Not a single type of notification works on these apps. Does anyone have any other suggestions? Any help would be appreciated. I really hope it's fixable and not just a matter of my phone being too old, because 3 years is not that old. Thank you!