Why my iPhone not supported Facebook

Facebook requires iOS 13.4 or later. 

iOS 12.5.7 is the latest iOS security update for iPhone 5s, 6 & 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.

You do not list your location. Sadly, some countries have banned access to Facebook and other social networking sites. A quick Google search shows bans in China, Iran, North Korea, Uganda, Russia and the UAE. Hopefully this does not affect you.