The iPhone 12 comes with the ability to use dual SIMs with a physical SIM card and an eSIM, it would appear that 5G will not be supported by dual SIM mode at launch.
When the new iPhone 12 and 12 Pro handsets go on sale this Friday they will not support 5G in dual SIM mode, this feature will apparently be added later on.
The news comes from an apparent internal document that was shared on Reddit, you can see the an excerpt from the document below.
“Does 5G work with Dual SIM?”
When using two lines in Dual SIM mode, 5G data isn’t supported on either line and will fall back to 4G LTE. If customers are using eSIM only and are on a 5G supported carrier and service plan, they’ll have 5G access.
So it looks like 5G will only be supported with a single SIM card at launch, Apple will apparently enable this feature later this year.