在你的对象完全初始化之前，你将self传递给CBPeripheralManager的初始化器。如果你将代码改为这样，它将编译：

import CoreBluetooth
        
@objc
public class L2CapChannelManager : NSObject, CBPeripheralManagerDelegate {
               
    private var peripheralManager: CBPeripheralManager?
    private var deviceConnectedMethodChannel: FlutterMethodChannel
            
    @objc
    public init(deviceConnectedMethodChannel: FlutterMethodChannel) {
        self.deviceConnectedMethodChannel = deviceConnectedMethodChannel
        super.init()
        self.peripheralManager = CBPeripheralManager(delegate: self, queue: nil)
    }
}

另一种解决方案是通过使用lazy属性来延迟CBPeripheralManager的创建：

import CoreBluetooth
        
@objc
public class L2CapChannelManager : NSObject, CBPeripheralManagerDelegate {
               
    private lazy var peripheralManager: CBPeripheralManager? = {
        CBPeripheralManager(delegate: self, queue: nil)
    }()
    private var deviceConnectedMethodChannel: FlutterMethodChannel
            
    @objc
    public init(deviceConnectedMethodChannel: FlutterMethodChannel) {
        self.deviceConnectedMethodChannel = deviceConnectedMethodChannel
    }
}