Select Widgets in the left side bar and drag the clock widget onto the canvas.

You can choose between analog and digital on the right sidebar. For both clocks, you can set the region, timezone and have the clock show the location.
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On the analog clock, you can set the theme to be either light or dark.

For the digital clock you can select:

If you include the date, you'll be given more options for how you can format it, whether it's written in European or American style, how it's positioned or whether you want it to be more compact.