Google Pixel 3 XL

Starting from the Pixel 3a, Google phones support the "Dual SIM, Dual Standby" mode. When there are no calls, both SIM cards remain on standby.
When you make a call, you can choose which SIM card to use, as well as which card will handle data.
If a call comes in on one of the two SIM cards, the phone rings and you can answer, while the other SIM is temporarily deactivated during the call.
Once the call ends, both cards return to standby mode.

For more information, visit the official Google support page: https://support.google.com/pixelphone/answer/9449293?hl=en