Why I can’t downloaded ios14

For an iPhone 7 Plus, you can update to iOS 15.7.6. To accomplish that, please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

The iPhone 7+ can use iOS 15.7.X. When updating iOS, you are required to update to the latest version available for that device.

Go to general and software update if you see there update then download.

i need to download ios14 because I need some app on my phone