I have application that already uses BLE. I know bluetooth 5 is supported on iPhone 8 and iPhone X. Client wants me to add support for bluetooth 5. I found that CoreBluetooth can be used only to "Communicate with Bluetooth 4.0 low-energy devices". How can I use Bluetooth 5.0 on iOS?
At the time of writing this, Apple has not provided API support for Bluetooth 5 functionality or any of its features (e.g. Long range, 2xSpeed, LE Advert Extensions, etc), so there's nothing you can do at your end. Currently only Bluetooth 4.2 features are supported (e.g. Data Packet Length Extension, LE Secure Connections, etc). Please have a look at the links below:-
https://developer.apple.com/videos/play/wwdc2017/712/
https://developer.apple.com/bluetooth/
I hope this helps.