Since a while (10.14? 10.15?), macOS requires applications to explicitly request certain permissions before being allowed to perform corresponding actions.

Accessing bluetooth is one of the things that require permissions.

The bluetooth examples need to have

<key>NSBluetoothPeripheralUsageDescription</key>
<string>A user application wants to access bluetooth.</string>

in their Info.plist file. Otherwise they will just crash when they try to access bluetooth.

Note that testing the example from Qt Creator is not sufficient, because macOS then checks Qt Creator's permissions instead (for some reason), which it has.

Also note that, when testing, bluetooth will only work after the application has been signed. But it no longer crashes after it has the correct entries in Info.plist.