That notification appears for any keyboard app, it isn't specifically about GBoard.
You are free to disable internet access for the keyboard and it can't send anything out.
Discussion
Ok. I think that's what I am going to do. Thank you!Maybe you've shared that before where do I disable the internet access fot it? May e that's why the Yandex and other keyboard wouldn't download my other language. If I forgot and did the internet disable thing.
When you download an app it gives you the choice to enable/disable on the install dialog.
Otherwise, go to Settings -> Apps -> All apps -> (the app you choose) -> Permissions -> Network
Ah ok. I already unchecked Network Permissions when I installed. Thank you, for confirming that's the same thing.