There is much talking around about Pixel 3a Dual Sim Feature. until now google hasn’t decided to give full support for Dual Sim Dual Standby (DSDS) to Pixel 3a.company just announced official support of Dual Sim feature on the Pixel 3a and Pixels 3a XL, offering the ability to use dual sim simultaneously.
you can use dual sim functionality with one physical SIM and one eSIM.giving users to receive and send call and message without deactivating other SIM
|Image Credit: DroidLife with Link Below the images|
to activate secondary SIM you”ll have to either set up an eSIM using the instructions provided by Google or put a physical SIM card if you connecting your network using eSIM once all thing sets up you are good to go, the phone will show message weather to choose between two sim to which will be your default sim to send call and message
Google support page also mentions that this feature will not be available in Japan.