All settings and configuration for the eero network are pushed via the internet.
When you are creating an your eero network for the first time, you will need a mobile device with an internet connection. This could be from an existing Wi-Fi network (if this is available throughout the set-up process), or it could be from your mobile data connection (4G/5G).
You are unable to configure the eero network without the eero app, or a data connection from the eero app.