It depends on how the developer chooses to implement the notifications and on how the app is distributed. The Play Store distribution of Signal uses Firebase Cl

It depends on how the developer chooses to implement the notifications and on how the app is distributed. The Play Store distribution of Signal uses Firebase Cloud Messaging (via Google Play Services or microG) and falls back to WebSockets if FCM is unavailable. The website distribution[1] of Signal only uses WebSockets. I don't think Signal tries to detect whether the phone is Chinese, only whether FCM is available. Since Google services (including FCM) are blocked in China, apps that serve both Chinese and non-Chinese users usually find some way to support both FCM and the Chinese equivalents. For example, Airbnb serves users both inside and outside of China, so they distribute two builds of their app. The Play Store distribution of Airbnb relies solely on FCM for push notifications. The Chinese distribution of Airbnb,[2] according to an App Manager[3] tracker scan, bundles push notification libraries from JPush,[4] Xiaomi, Huawei, and Vivo. Developers can choose to have one app distribution that support all of these services, or they can release separate builds that each handle some of these services. This varies from app to app. [1] https://signal.org/android/apk/ https://signal.org/android/apk/ [2] Visit https://www.airbnb.cn https://www.airbnb.cn on an Android phone and the download banner appears at the bottom. [3] https://github.com/MuntashirAkon/AppManager https://github.com/MuntashirAkon/AppManager [4] https://www.jiguang.cn/en/push https://www.jiguang.cn/en/push