If you click the hamburger icon (3 horiz. bars), then New Message, you should see Calendar... as one of the choices.

I do not have this menu item (I am using latest version (see attached image).

Sorry about including same image 3 times, The image did no show up in preview so I tried a couple of times.

Have you installed the calendar Lightning. That would be the first step.

Installed plugin from https://www.mozilla.org/en-US/projects/calendar/ and it shows up as active in Extensions.

The images that you posted show you opening the AppMenu button list but you need to click Mew Message to open that menu.

I know! New Message? That is silly. You are right. The programmers completely messed up the new, and hardy improved, menu system. I recommend you do yourself a favor and turn the old Menu Bar back on and use a real menu system.

Press the alt key to make the menu bar appear. From the Menu Bar select View-Toolbars and click Menu bar back on. Now Calendar is where is belongs and where all the documentation says it is. File-New-Calendar

Maybe I should ask another basic question. Do you have the Calendar tab open showing the default calendar? If not from the menu bar select Events and Tasks-Calendar to open the calendar tab. The shortcut is control+shift+c

Thanks, that is great. turned on proper menu and got calendar working and linked to goggle calendar easily. Mucho thanks.