If you specifically want /e/OS, you need to watch out where you buy the Fairphone.
There is two versions, with the regular Android (with Google services) version being the more common one.

https://www.fairphone.com/nl/the-fairphone-gen-6-e-operating-system

If you buy this one from their website you are guaranteed to get the /e/OS version

Edit: Also worth noting that you could also unlock the bootloader, and install /e/OS on the regular Android version as well. You might be able to save € 150-200 that way.

To my knowledge you can relock the bootloader after you are done? You'd have to look into that yourself though.