One eSIM covers 34 countries. Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey, the United Kingdom and Vatican City.
You do not pick a country when you buy. The eSIM connects to whichever partner network is strongest where you are standing, and it keeps working when you cross a border, on the same plan and the same balance. A train from Paris to Milan does not need anything from you.
The full list with the host network in each country is in the Countries panel further up this page, pulled from the live plan rather than typed out once and left to rot. If a country is not on that list, it is not covered, and the section below tells you what to do instead.