Add Gmail to Outlook: "This browser or app may not be secure"

While adding a Gmail email account into Outlook. A screen might pop-up saying:

Couldn't sign you in This browser or app may not be secure. Learn more

This happens during first time setup, or whenever you go to File > Add Account > enter gmail.com address and click connect.

The rest of the message reads:

Try using a different browser. If you’re already using a supported browser, you can refresh your screen and try again to sign in.

Outlook appears to be using Internet Explorer or its engine internally instead of the user set default browser to login to Gmail.

In my experience, installing all operating system updates helps alleviate this issue. However, if this is not possible in the current situation, the solution below might help.

Press Windows key + R

Type in regedit

Browse to Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BROWSER_EMULATION

Right click > DWORD (32-bit) Value

Name: OUTLOOK.EXE Value: 11000 (DWORD, decimal)

If this doesn't help, try doing the same for the keys down below

HKCU:

Computer\HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BROWSER_EMULATION

32bit emulation:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BROWSER_EMULATION

This forces Browser Emulation (compatibility mode) to IE 11 which supports Google sign in.

Problem solved for you? Let me know in the comments down below!