How were the calendars added, with the Provider add-on or the built-in CalDAV protocol?

The built-in one. I don't have the Lightning extension.

L

Is the Calendar Pane showing? It's enabled under View/Calendar/Calendar Pane on the Calendar tab. Press Alt if the Menu Bar with View is hidden.

Yes, it appears, as you can see in the screenshot. But normally, there is a list of all the calendars I'm subscribed to. Also, if I add appointments to my calendar, the information updates. However, I added new calendars to my Google account and I want to add them to my view. But when I wanted to do that, I discovered I couldn't see my calendars anymore.

L

If you right-click in the blank space below the mini-month, Show All Calendars, do they appear?

It's always worth seeing if the same thing happens in safe/troubleshoot mode (hold Shift when launching TB).

Well it was a problem with my eyes... when I right-clicked under the mini calendar nothing happened. I think I had tried it before with no result either. But your comment made me look a little deaper and I noticed that the list of calendars was unchecked under View > Calendar > Calendar Pane. Checked it and now I'm back in business!

Thanks!