I was a bit apprehensive when I noticed you added a login button, as I've always found AnkiDroid's logging-in-doesn't-initiate-a-sync to be confusing. But I've gone back and checked, and I think the main issue there is the login screen is shown when the user taps on the sync button, so my expectation is that a sync will happen. If the user logs in from the preferences screen, I guess that's not going to be as much of a problem. But it may still be worth displaying a dialog box after a successful login, to remind the user they'll need to close Anki or click on the sync button to sync for the first time. What do you think?

As of 2.17, logging in via the onboarding process initiates a (download) sync.

I'd support the above as a UX enhancement

Originally posted by @david-allison in ankitects/anki#2994 (comment)