What is the menu item Automatic Updates for iOS when you have to start them manually?
Refer to the Apple Support document, Update your iPhone, iPad, or iPod touch:


  Update automatically
  
  With iOS 12 or later, or iPadOS, you can have your device update automatically. To turn on automatic updates, go to Settings > General > Software Update, then tap Automatic Updates. Your device will automatically update to the latest version of iOS or iPadOS. Some updates might need to be installed manually.


Here's the conditions to be met for automatic updates to install: