I've used the Airalo app to buy data-only eSims in multiple regions, and they have global ones also. I would guess it's not as cheap as you'd get if you waited to buy from local providers in arrival, but it's very convenient.

+1 to Airalo. The country specific ones are super cheap. $7 for 2GB or something like that?

I once did the 30-day Global one for I think $20 for 4GB or so. Worked all over Europe + Middle East. Was very impressed.

Eskimo has a 2y global SIM, excluding a handful of countries, https://news.ycombinator.com/item?id=40382377