I I need 13.4 version to upload Facebook apps

An iPhone 6/6 plus can't be updated beyond 12.5.7, it doesn't have the hardware needed to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.

Facebook will not install on your phone, use the web version.

You don't say what iPhone model you own, but I would guess it's iPhone 6 or older. An iPhone 6 cannot run anything higher than iOS 12.5.7. If you need a phone which can run a higher iOS version, then you'll need to retire your very old iPhone and buy a newer, more modern iPhone.

a l I need 13.4 version to upload Facebook apps