Qualcomm is rushing to deliver the X55 5G modem, designed to connect to the true 5G standalone core. The current combination, of a Qualcomm Snapdragon 855 application processor and X50 modem, will not be acceptable on Chinese networks after 2019. China has decided that 5G phones must be able to connect to the standalone 5G core, which the X50 does not do.
All current 5G systems use 5G for the phone connection but run on the 4G core. They are called "non-standalone" 5G, requiring a 4G network in place. The true 5G core, named "standalone," is not yet ready, but China wants to switch over as soon as practical. China Mobile is hoping for the first quarter of 2020.
The SA core is required for "net slicing." It also has many features that aid software-defined networks and other advanced technologies. But SDN is moving forward without the 5G SA core and it's not clear anyone will want to pay for network slicing QOS for years. Nearly everyone in the West is going slow on 5G SA.
Huawei's Mate-20 5G does support SA.