The Huawei headset may not connect to the Apple 12 due to incompatibility or incorrect Settings. First, make sure the headset is in Bluetooth pairing mode and has been disconnected from other devices.
Then, turn on Bluetooth on your iPhone 12, search for and select Huawei headphones. If you still can't connect, try restarting your Apple 12 and Huawei headphones and make sure there are no obstacles between them. If the problem persists, contact Huawei or Apple customer support.