Thanks, I think the description of what happens if you insert the nanoSIM was the missing piece.

I guess another option would be to install another eSIM and toggle between that and my T-Mobile.

Actually for one trip I'm planning in September, I would cross from Switzerland to the Chamonix area where they may or may not have shops selling physical SIM cards. AT least not through a carrier store.

And I don't think Swiss SIM cards will roam in neighboring France.

So I was looking at getting a French SIM sold on Amazon. But it would be cool if I could get an eSIM for France.