I've uninstalled, reinstalled

You've been wasting your time. Profile files are stored separately from the Thunderbird program files. The program files are static and do not change (except when you upgrade the Thunderbird application version). Because we store profile and program files separately, you can uninstall Thunderbird without losing your messages and settings, and if something goes wrong with a Thunderbird update your information will still be available. It also means that you don't have to reinstall Thunderbird in order to delete your information or troubleshoot a problem.

I've ... tried everything I could find online

So what else did you do?

nothing enables my calendar in 78.7.0!

What type of calendar is it - local or network? If network type, is it a Google Calendar? If Google, how do you access it? How do you determine the your calendar is disabled?

Thank you for the reply and information. I read that a calendar is built into 78.7, that lightning was not required. Is this information incorrect? To answer you're questions, I have not added a calendar to thunderbird, I've always used the calendar that was installed during normal installation. Now it's gone and all of my meeting requests come through 1 hour off. I read you can fix the time zone in calendar however, as you know, I don't have a calendar installed.

Any help you can provide would be greatly appreciated. I've made many donations to Mozilla over the years, one recently.

Mark

I read that a calendar is built into 78.7, that lightning was not required. Is this information incorrect?

Kinda. It's still Lightning, but not as an extension bundled with Thunderbird, but fully integrated into Thunderbird.

I've always used the calendar that was installed during normal installation.

So then this is a local calendar?

Now it's gone

You'd need to explain that in more detail. When opening the calendar tab, what do you see in the left pane? A screenshot may help. https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

all of my meeting requests come through 1 hour off.

Are you talking about meeting invitations you receive from someone else? How do you determine they are 1 hour off?

I read you can fix the time zone in calendar

I'm not sure what you're trying to fix. To set the calendar timezone: At the top right of the Thunderbird window, click the menu button > Options > Calendar