How to disable the physical simulator and only use the eSIM on iPhone XS / iPhone XS Max?

You can remove the physical SIM card from the holder. The phone will continue to work and you can use the eSIM to access the operator's services.

If you do not have an eSIM yet and you want the same operator for the eSIM, check your provider's website or the support contact. Sometimes it is possible to transfer your subscription for free to an eSIM instead of a physical SIM, leaving the SIM slot free for other operators to use when traveling.

However, not all operators support eSIM, so your mileage may vary.