Yes, the default is more than single-spaced. It is because this is easier to read.
Change Default Settings by Suzanne Barnhill, MVP

And, by the way, the default font is changing from Calibri to Aptos. Suzanne's page deals with making it permanent for documents created based on the Normal template.
You may want to create and use your own custom Theme, which will have the fonts you want in all built-in Word styles.

Here are some references that should help you if you regularly use Word to get your work done.

• [Quick] Style Sets and Word Themes in Microsoft Word
• The Importance of Styles in Microsoft Word
• Basic Concepts of Microsoft Word - from Shauna Kelly
• Templates in Microsoft Word