5G network will not initially be available in Dual-SIM mode
One of the biggest novelties in this year's iPhones is the introduction of 5G network support. For the vast majority of people this is very good news. However, there is an exception.
Unfortunately people using two SIM cards will not have access to 5G network. This is due to internal Apple documents, which have been sent to stores and mobile networks. In case of two active numbers, the maximum network that will be available is 4G LTE. If the owners of new phones will only use a physical SIM card or its electronic version, then the antennas will receive signals from the 5G network.
Apparently this limitation is caused by the currently available software and this problem is to be solved with a newer version of the system. This is expected to happen later this year. For the time being, Apple has not responded to this information.
Source: MacRumors