Thunderbird Version 90.0b1 opens to a blank semi transparent screen

Thunderbird 89.XX was updated on 6-4-2021 to 90.0b1 and is now broken. This update was applied automatically, a restart of Thunderbird was performed and now starting TBird results in a mostly transparent box in the middle of the screen. No data/text, etc is in the box, completely blank. I have a screen shot if that helps.
I also have the diagnostic report that was generated by TBird 90 after I was able to start it in Safe Mode.

Windows 7 64 bit on an HP desktop, was working properly until this update

Are you using Conversations add-on? AIUI it is broken in beta 90.

I will go look today. My neighbors are very basic in their needs. I do not believe any add-ons have been installed. Will double check.
Thank you