Where is "Empty Trash" in the "Trash" right click context menu

It is right where is always has been. See image.

Is it possible to do a reinstall of TB to default, without loosing any of my e-mail or address book information?

The Thunderbird program is separate from your data which is in your profile. You can reinstall Thunderbird and retain data. That being said, making a backup is always a good idea. This tells you about your profile. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data

Unfortunately, your image didn't show up. I finally found it in your support reply. But after searching the context menu's on all of the initial folders I did find it in the Archives context menu. See the attached image. I also found it in the Local Trash context menu. But again not in the main trash menu. Is there any way to get it back into the main Trash context menu? Thank you for the information on the reinstall. I will not list this as solved yet.

When was the last time you restarted your computer?

Start Thunderbird unsafe mode. You can do this from the help menu or by holding the shift key when launching Thunderbird.. Your installation has issues.

The computer is restarted daily. Should I disable all add-ons and reset toolbars and controls?

That would be starting in Safe mode as suggested.