Change Font Book preferences on Mac
Use Font Book preferences to change options for where fonts are installed and how duplicates are handled. To change these preferences in the Font Book app on your Mac, choose Font Book > Preferences.
Default Install Location
Choose where to install fonts:
System fonts you download from Apple aren’t installed in these locations.
Resolve duplicates by moving files to the Trash
Font Book moves duplicate fonts to the Trash when it resolves duplicates. If you don’t select this option, duplicate fonts are disabled, but not removed.
In some apps, such as Mail or TextEdit, you can select a font to use as the default in the app. For more information, search the built-in help for the app.