I have ordered a phone with an eSim this week and I have been reading a bit into it.
As far as I know so far, you just have to download an app and you can just book some extra data as needed - it seems especially cool because you can just book a local plan when you're abroad instead of getting a local sim card. Which can be more or less a hassle - 2019 I went to South Africa where it was pretty easy to get a sim card at the airport, 2018 I went to India, where it was a hassle.
I guess for people in the US this is not a problem? Some of my friends have global contracts, and I had that too when I was there via googles project fi. We don't really have an equivalent in Germany
I found the following pages in case anyone also wants to look into it
https://esimdb.com/ - this is an overview page about different esims
https://www.airalo.com/ - this is one specific offer that seems to be the cheapest for Germany, which is where I would try it, since I live here haha