According to the current information, the Kirin 820 can be upgraded to Hongmeng 4.0. Huawei has already announced that it will roll out the HarmonyOS upgrade on some Huawei and Honor phones starting in 2021, and the Kirin 820, as one of Huawei's flagship chips, is also expected to be supported by the upgrade. However, the specific upgrade plan and schedule may vary by region and specific model, so you are advised to pay attention to Huawei's official notice for relevant updates.
At present, whether the Kirin 820 processor can be upgraded to the Hongmeng 4.0 system has not been confirmed. Huawei has not released the list of supported devices for the Hongmeng 4.0 system. You are advised to pay attention to relevant news released by Huawei or contact Huawei customer service for more details.