Post a screenshot of the popup.

This is what pops up when I open Thunderbird

I suggest you try disabling any antivirus that is scanning encrypted connections and try again. The two pages are web pages served by google, just as they would be it you used Firefox.

That the second page it suggesting a malformed response, the first this to try is elimination things that may be changing pages or responses on the fly. Hence my suggestion of antivirus. Although I am not aware of defender having caused issues with modifying paged, most of the third party products have just such a reputation.

I have disabled my antivirus and still no change. I can log into Google email through Mozilla without any problems if that makes any difference. I even re installed and recovered my profiles from a backup and still the same. I am at a loss here?

I have figured out the problem. I had to enable third party cookies in the settings. I think it got changed when I was checking something out in the settings. Thank you for your help. Much appreciated!

I just cleaned all the cookies and the problem was solved Settings>Web Content>Show cookies>Remove all

Thank you for your response here, however I figured the issue out back in September. It turned out to be Third Party cookies needed to be enabled.