You can insert a degree symbol (among many other symbols) by using the Special Characters menu, which is now called the Emoji & Symbols menu in more recent versions of macOS, including macOS Mojave.
You can also insert it using Edit > Emoji & Symbols or by typing degree You can also insert it using Edit > Emoji & Symbols or by typing \degree and hitting space
Home Degree symbol Mac How to type degree° symbol on Mac: Quick methods - iGeeksBlo