Bluetooth vs BLE

It is not a question of Swift or ObjC.

And effectively, framwork let you discover only BLE devices (ie BT 4.0, not legacy ones).

The Core Bluetooth framework provides the classes needed for your apps to communicate with devices that are equipped with Bluetooth low energy wireless technology.

In https://developer.apple.com/library/archive/documentation/NetworkingInternetWeb/Conceptual/CoreBluetooth_concepts/AboutCoreBluetooth/Introduction.html

The Core Bluetooth framework provides the classes needed for your iOS and Mac apps to communicate with devices that are equipped with Bluetooth low energy wireless technology. For example, your app can discover, explore, and interact with low energy peripheral devices, such as heart rate monitors and digital thermostats. As of macOS 10.9 and iOS 6, Mac and iOS devices can also function as Bluetooth low energy peripherals, serving data to other devices, including other Mac and iOS devices.

At a Glance

Bluetooth low energy wireless technology is based on the Bluetooth 4.0 specification, which, among other things, defines a set of protocols for communicating between low energy devices. The Core Bluetooth framework is an abstraction of the Bluetooth low energy protocol stack. That said, it hides many of the low-level details of the specification from you, the developer, making it much easier for you to develop apps that interact with Bluetooth low energy devices.