Not sure why you attracted downvotes with that comment. It's 100% correct. You can buy an eSIM while still in the US and just leave it turned off, then flip it on when you get to your destination. Some providers do still advise waiting to install the eSIM until after you reach their home territory, but that's not any more difficult.

We just did exactly this a couple weeks ago when we went to the UK & France. Super easy, as soon as the plane took off I toggled roaming off on my regular US line, and turned on the traveling eSIM when we landed. Bam, phone works as normal, still gets calls and texts, etc, but way cheaper than paying roaming charges.