So, a bit more info - learning as I go ... this market is always changing and Im always behind, apparently!
So, the eSIM product (a programmable chip already in more recent phones that is programmed to be a SIM by a QR code sent to your email after purchase - or perhaps even in real time by a rep at an airport or shop) is very interesting, but so far I have not been able to determine if it ("it" could be several different carriers in Europe) supports international calling.
The eSIM, like any dual SIM concept could also introduce another level of complexity into the experience - looks like you have to specify which SIM you are using, the physical nano SIM, or the eSIM.
Unless I find something that really simplifies the dual SIM (one SIM and one eSIM) approach, we'll probably just buy the $50 plan from T-Mobile which provides international calling and 4G (supposedly) data speeds. The Do Nothing option would still allow really slow data (we use phones for navigation, translation, where to eat, checking email, news, etc) - but some of that including calling could be via WiFi calling at hotels, etc ... if the $50 plus up option works really well, it is the clear winner - we'll see!
We are possibly going to France this fall so I was researching the same issue with our T-Mobile phones. It seemed to be as easy as buying the international data package. Is that what you understood? No different SIM card required?