Carrier Dual Sim Primer? Especially for travel outside of North America?

[dmfresco]

I have an unlocked iPhone 12 Pro on T-Mobile. A few years ago, prior to iPhone XS or so, I had great success purchasing a SIM card in India and using it during my travels. In hopes of one day traveling abroad again, I wonder if there is a place to learn about Dual SIM/eSIM for the purpose of getting say a month of data, text, calls in the country of destination while letting the T-Mobile SIM roam free (or with their International upgrade for the month). If this option exists, is it a non-contract month? A pre-paid month? I am mostly hoping to get 4G/5G data for the time in country, more so than making calls. Finally, is it possible to establish the service in advance from the States so that it's ready when I arrive in country?