Unable to add my first Google account

[Kunal Ashar]

This is a fresh/new Windows 10 laptop with the all the latest updates. I am unable to add my first [Postbox-registered] Gmail account, as Postbox keeps saying "Postbox failed to find the settings for your email account".
All malware/AV/firewall settings are off.

Postbox tries to find the right settings for Gmail and fails (the settings it shows are clearly wrong). If I "correct" the email settings, Postbox tries to authorize itself in my browser, and the browser apparently succeeds, but Postbox still fails.

On the same laptop, adding my Gmail account to Outlook (and another client called BlueMail) works perfectly. It's just Postbox that cannot authenticate correctly with Google.

Any ideas?