Do you mean the release notes? Can you post a screen shot https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem

Yes, I post the screenshot. Thank you.

Does problem go away if you start in safe mode?

 https://support.mozilla.org/en-US/kb/safe-mode-thunderbird

If it goes away, then the problem is a theme or other addon

Perhaps it is. However, I cannot restart because I cannot access the menu of Thunderbird. If I click on the upper right corner the X to exit, I can exit but the moment I start Thunderbird, the notes page comes back. I use Walnut as the addon/theme. Any suggestions please? Thanks.

I could finally remove Walnut/Walnut 2. They cause Thunderbird V. 45 to freeze. The solution was a dirty one. I clicked on the first Thunderbird page before the Notes page opened. This way the Notes page became a tab. Then I went into safe mode and saw that the problem disappeared. I could go to safe mode by again quickly clicking on the first Thunderbird page (input page for me) before it freezes. So, a lesson to be learned from this for me is that Add-ons may cause significant problems as the new versions of Thunderbird come online. Hope this helps others. Thank you for your help.

thanks for the update.

for future information, you do not need to have thunderbird running to get into safe mode. from the support article "If Thunderbird is not running: Start Thunderbird in Safe Mode by holding down the Shift key while starting the application."