Is your Event Toolbar hidden? You can reveal it from the View menu. See attached image.

My View menu does not list that under View->Toolbars, just Menu Bar, Spaces Toolbar, Status Bar, and Customize... are active.

Are you looking at a New Event window, the one I show in the image? Double click a Day square or choose "+ New Event" from the Calendar Pane. If not, please provide a screen shot.

Not there. Is that a cell phone image? I'm using a laptop.

No. This is both a Windows desktop and laptop. See image...

I restarted Thunderbird and now it's on the View menu when I open a new event. Glitch.

I see why your images look like they may be from a cell - your new event opens in it's own window, while mine shows up as a third tab in the main window, with email and calendar on the first two. That makes it look very different.

The "Save and Close" button should be available in either view.