well there are release notes. https://www.thunderbird.net/en-US/thunderbird/60.4.0/releasenotes/

But injecting a fake on the day of a real update is clever. Why didn't the INFO link work? Why hasn't it popped up again since I said "tell me later"

did you read the release notes? This has been ongoing since the 20th DEcember. IT might be another 2 weeks or more before your number comes up again.

I suggest you turn your paranoia dial down however. Thunderbird is notifying you that an update is available on it's update servers, it is not a phishing email advising you to please enter your bank password and secret code.

Why did the link not work. I have no idea. but the one in the previous version had the same problem

While the cause may be different, the symptom is the same as the one discussed at https://support.mozilla.org/en-US/questions/1048562, except that no tabs ever opened. I had to manually go to thunderbird.net and click on the "What's new" link. The pop-up telling me that 60.5.0 was available had the same problem. And if I recall correctly, the problem goes back further than the pop-up for 60.4.0.

I got another update popup yesterday & the "more info" link did nothing.

This is a continuing security issue, since if people get used to not being able to goto the Mozilla site, its easier to get people to install something malicious.

VerizonSucks said

I got another update popup yesterday & the "more info" link did nothing. This is a continuing security issue, since if people get used to not being able to goto the Mozilla site, its easier to get people to install something malicious.

Well File a bug report! https://bugzilla.mozilla.org/