In Android majorly banking apps for primary sim to be the registered phone number, is that the same in iPhone or can I use my registered number as e-sim and have the primary physical sim slow empty? Follow up question, folks who own iPhone how do u manage to switch to new sim when you travel abroad?

iPhones support multiple esims. So you can add multiple numbers as esims but only one can be active

iPhone 13+ supports two active esim. I’ve been using my Airtel esim for quite some time

I use Airtel connection with the e-SIM. When travelling (or otherwise needing to access another number) I pop-in a physical SIM in the tray. Physical SIM is easier and quicker to swap (for me), hence this setup. And this is with iPhone 13 Pro.

@miniature-exabyte-51670 AFAIK in iPhone there is no concept of primary and secondary sims.