Why I can’t download Facebook anwhyvd instagram on my iPhone 6

Both apps require iOS 13.4 or later. Your iPhone, which supports up to iOS 12.5.7, is not compatible with these apps.

Your iPhone cannot update to iOS 13 or later due to your internal hardware being too old to support it.

Apple ended major software update support for your iPhone in September 2019 - although it continues to receive security updates - with the most recent being iOS 12.5.7, released January 2023.

Many app developers have dropped support for iOS 12.x in its apps, often because the APIs in its apps have updated to the most recent version, making this iOS version not compatible.

The iPhone 6 is almost 9 years old.

iPhone 8 and later models are capable of supporting iOS 16.

You may consider buying a new iPhone. Even the entry-level iPhone SE can run the latest iOS version, iOS 16.5.

Here is a list of unsupported iPhones with max iOS supported:

Model            Architecture  Introduced       Max supported iOS
iPhone (1st)     32-bit        June 2007        iOS 3.1.3
iPhone 3G        32-bit        July 2008        iOS 4.2.1
iPhone 3GS       32-bit        June 2009        iOS 6.1.6
iPhone 4         32-bit        June 2010        iOS 7.1.2
iPhone 4S        32-bit        October 2011     iOS 9.3.6
iPhone 5         32-bit        September 2012   iOS 10.3.4
iPhone 5C        32-bit        September 2013   iOS 10.3.3
iPhone 5S        64-bit        September 2013   iOS 12.5.7
iPhone 6         64-bit        September 2014   iOS 12.5.7 <- Your iPhone model
iPhone 6 Plus    64-bit        September 2014   iOS 12.5.7
iPhone 6S        64-bit        September 2015   iOS 15.7.6
iPhone 6S Plus   64-bit        September 2015   iOS 15.7.6
iPhone SE (1st)  64-bit        March 2016       iOS 15.7.6
iPhone 7         64-bit        September 2016   iOS 15.7.6
iPhone 7 Plus    64-bit        September 2016   iOS 15.7.6