Why can't I update my iPhone to iOS 13.4?

iOS 12.5.7 is the latest iOS security update for iPhone 6 Plus

Go to Settings -> General -> Software Update -> Download and Install (if you haven't already done that).

iPhone 6 Plus can’t be update to a higher iOS (13 and later). 

Yes, most apps require iOS 13.4 or later.                                

Considering a newer type of iPhone?

Read this before you buy a newer type iPhone.

Bummer.

Unfortunately, your iPhone 6 Plus is not compatible with iOS 13 or higher.

That model can be updated to iOS 12.5.7, no further.

My phone can’t apdate software