Can I use an eSIM and a physical SIM at the same time?

You can run the eSIM and your physical SIM at the same time if your phone takes two SIMs. Every iPhone with eSIM, from the XR and XS on, runs both together; iPhone 13 and later can also run two eSIMs at once.

Not every device has eSIM. Most recent phones from Apple, Samsung and Google do; many other new phones still do not. Tablets, smartwatches and laptops have it less often, and usually only in the Cellular or 5G version.