"This applications requires iOS 13.4 or later"

It sound like you have an older iPhone that has not been updated … or is not able to be updated. Please select Settings > General > Software Update. If your phone is eligible for an update, you will be prompted to do so. If it will not update, please reply, telling us which iPhone you have and what version of iOS you have.

You can find more information here:

Update your iPhone or iPad - Apple Support

Im sorry you can use Facebook app because your iPhone 6 plus is old and it cant upgrade to iOS 13 or 16

you can only be in iOS 12.5.6

But you can use Facebook web

Iphone 5s

IOS 12.5.6

MaraPeshterlieva wrote:

Iphone 5s

IOS 12.5.6

Yes, that is the highest possible for that model.

I can`t dowload any apps. How can I do it