iPhone 13 international usage eSim and SIM card??

I have an iPhone 13 pro, T-Mobile, with eSim. I'm traveling to Italy in September. While T-Mobile allows you to just "turn your phone on" in most countries, the data services are/were dreadful. On a trip in 2017 to Italy, the best data I could get was 2G. Usually it was less than that, and it was for all intents, useless.

I know I can buy a plan for a few weeks from T-Mobile, but I don't know if they use the best carriers in Italy and what the data availability is particularly in Sicily. If it is anything like 2017, it's awful. I need to use the maps feature so good data is essential. So is iMessage and What's App.

I was told by my Italian friend to buy a Vodafone SIM card over there, but since I have an eSim, I don't know what will happen by just placing a physical SIM card in the phone. Will it wipe the phone or will I have to do a reset? What will happen upon my return to the USA; will I just remove the physical SIM and all will be back to normal, or will I have to go to a T-Mobile store for "provisioning" or some other kind of wacky stuff?

Any ideas would be appreciated.