Google 2-step verification and Gmail notifications

I'm using Mint 19.3 Cinnamon and until recently have had no problems receiving notification of Gmails when they arrive.  I use T-Bird as my desktop client but the notifications used to appear on my desktop, even without T-Bird being open - both an alert sound and a notification on my taskbar. 

Since being made to use Google 2-step verification the notifications no longer appear, although the new emails are added to the IN-box as usual.

Is this change likely to be as a result of the change in Google security?  I have the problem on both my laptop and desktop machines - same setup on both.

I'm not sure as there has also been an update to the Mint kernel very recently so this may also be the cause.  I haven't tried reverting the kernel yet - just wondering if anyone else has noticed this change.