MacBook Air and iPhone 8 Plus

Hi I have two questions. First question is my iPhone 8 Plus had the latest update and most of my apps are not letting me get notifications when someone sends me a message. How can I get my notifications back on? I tried going back to the apps and resetting the notification in the app and that still didn’t work.

Second question is from my MacBook Air 2012 is not updating, pretty much hasn’t been updateding for years and I was wondering if I could get an update so I can keep my laptop?