First question is do you have the Thunderbird calendar, Lightning, installed? Go to the Add Ons tab and click Extensions. Is Lightning listed and Enabled? If not enter Lightning into the search field and install it.

IF it is installed do you not have a Calendar tab shown with the main Thunderbird tab? if not from the Events and Tasks menu click Calendar to open Lightning into it's tab.

When I searched the add on for lightning, I got 766 hits, How I determine which is the one you are referring to?

Sounds like you did not use the search box on the Add ons-Extension page.

One thing that would help here is for someone to describe what steps need to be performed to view a calendar (of any sort) within Thunderbird after a new installation.

The chosen answer here seems to be "install lightning" but that is at odds with https://www.thunderbird.net/en-US/thunderbird/60.3.0/releasenotes/ and third-party info such as https://www.reddit.com/r/Thunderbird/comments/97sckx/lightning_5491_incompatible_with_thunderbird_60/ . https://support.mozilla.org/en-US/kb/calendar-updates-issues-thunderbird is unhelpful as it does not contain an answer to "how do I view a calendar after installing Thunderbird".

For completeness the steps that I've always performed (which worked until today) have been to install Lightning, install Provider for Google Calendar, and restart as required. However presumably this should be unnecessary if Thunderbird actually supports calendar functionality now?

If Lightning is installed and enabled, the calendar can be displayed from the main window under Events & Tasks/Calendar (press Alt if the Menu Bar is hidden), or Ctrl+Shift+C, or by clicking the calendar icon at the right end of the tab bar (see picture). The Provider add-on, like most add-ons, requires a restart to be enabled.

sfhowes said

If Lightning is installed and enabled

So to be clear what I was doing was correct - Install Thunderbird, manually install Lightning from the add-ons list and restart as required? (which would mean that Thunderbird does not contain native calendar functionality).

Lightning is included in the full TB installer, so it's not necessary to download a separate Lightning installer. Besides, the Lightning versions on the add-ons site are only valid for TB 52 and lower. However, even when Lightning is installed, it sometimes 'disappears', so the steps described in the support article above are helpful.

sfhowes said

Lightning is included in the full TB installer, so it's not necessary to download a separate Lightning installer.

OK, as a test I've created a new user account here (in KDE on Ubuntu 18.04) and logged in as that user. When I run Thunderbird there as expected it takes me through the "set up a profile" wizard. I've told it about a Gmail address and I can see some mail. How do I open a calendar?

Edit: To be clear at this stage for this user the only add-on installed by default is "Messaging Menu and Unity Launcher Integration 1.4" which seems to be a default in the Ubuntu package. I expect I'll need to add the Provider for Google Calendar add-on at some stage to access a Google Calendar, but I can't even see any local calendar access option. What menu is it on?

The support article re update issues has a section for Linux users. Apparently, the standard Ubuntu repository didn't include Lightning in TB 60, so you have to install the 'package':

https://support.mozilla.org/en-US/kb/calendar-updates-issues-thunderbird#w_i-am-on-linux-and-lightning-disappeared-after-thunderbird-got-updated-release-and-beta-channel

sfhowes said

The support article re update issues has a section for Linux users. Apparently, the standard Ubuntu repository didn't include Lightning in TB 60, so you have to install the 'package': https://support.mozilla.org/en-US/kb/calendar-updates-issues-thunderbird#w_i-am-on-linux-and-lightning-disappeared-after-thunderbird-got-updated-release-and-beta-channel

Yes - that did work for the new user account added above on Linux, although it didn't work for the existing user account from which calendar functionality "disappeared" (although the reset/remove etc. sequence described at https://support.mozilla.org/en-US/kb/calendar-updates-issues-thunderbird#w_lightning-disappears-after-a-thunderbird-update-release-and-beta-versions may have - it didn't work on Windows when I tried it but I didn't try on Linux).

I suspect that what I should have done (at the very start) on Linux was to install that package and have that available to all users and not install an add-on (for just one user), which caused problems when (a) that add-on stopped being supported any more and (b) I tried to get at a calendar from another user account. To summarise the answer to my own question it sounds like calendar functionality should "just be there" in a fresh Thunderbird installation on Windows, and also if the correct packages are installed on Linux.