Dashboard Catalina missing - how to get it back

If you are using a trackpad, a two-finger swipe moving from the extreme right-side of the trackpad to the left will slide the Notifications panel onto the main screen. Reversing this direction puts it away. This is a System Preferences : Trackpad : More Gestures option. It even works with the first generation (battery) Trackpad.

If no Trackpad, visit System Preferences : Keyboard : Shortcuts : Mission Control, select Show Notification Center, and in my case, I clicked None at the far right of this entry, and typed the F6 key. When I closed System Preferences, the F6 key toggled the entry/exit of the Notification center. See this article.

On Catalina, look at System Preferences : Extensions : Today panel and select the tools that are available. Once you have done that, then click on Notifications icon (top right) in the menu bar, and select the Today page.

I would not go through the risk, and minimal reward of reverting to Mojave for Dashboard widgets that virtually no developer continues to maintain. Dashboard is now 15 years old and time to move on.

If Apple has not provided a "Mini calendar" in the Today extensions, then you will need to sift through the Mac App Store for a relevant solution — if it exists. The items in the Today Extensions are not the old Dashboard widgets, so restoring them in Extensions : Today is out of the question, and someone, whether Apple or otherwise would have to develop a replacement for the Today panel.

The Dashboard is not coming back. I guess you will have to downgrade if you want it. I never used it when it existed.

F13 opens the Notification Center.

I just realized that you may not. You can reassign the key in System Preferences > Keyboard > Shortcuts.