We’ve recently received customer reports that they are unable to add Google accounts to Outlook once the Windows 10 Security Baseline is applied. When attempting to add a Google account, they see the message “Couldn’t sign you in. The browser or app may not be secure,” as shown below.
Google prompt in Outlook displaying a message "Couldn’t sign you in. The browser or app may not be secure".
This error is caused by a configuration setting within a Windows 10 Security Baseline.