If your iPhone or iPad is running iOS 16.4 or newer, your device may attempt to automatically activate your data package during the automatic installation flow, as long as it can connect to a supported network.
This is because devices running iOS 16.4 or newer no longer require "Data Roaming" to be manually toggled on, and eSIMs are able to instantly connect to supported networks.
During the eSIM installation flow, iOS devices try to make things easier for their users by doing the installation and activation all at once. So because there is no longer the need to toggle on "Data Roaming," any devices running iOS 16.4 or newer will automatically be able to connect.
So if you're already in the correct country, don't install your eSIM on an iPhone or iPad until you're ready to begin using the data.