Saving your favorite font as default is available in version 5.0.32 or later. Once you click on the Text tool, you will see a new Styling icon on the right side of the toolbar.
Screenshot 1: GoodNotes 5 Toolbar
Two ways to save a font as default
Option 1: Setting a default font from the start
Click on the Text tool > Styling icon > adjust the font size and style to your liking and click on Save as Default before exiting.
Option 2: Changing the existing default font
Click on the textbox > use Select All and the text will be selected as shown in the picture. Then click on the Styling icon to change the font size and style to your liking. Click Save as Default before exiting.
Screenshot 2: Styling Settings
Changing a font temporarily
The changes you made in the font Settings are universal throughout your notebooks once you save it as default. To change the font style temporarily, you can select the whole sentence or a portion of the sentence and make the adjustment without saving it as default.
Screenshot 3: Styling a portion of the sentence
*Please note: If you want to copy an existing text document and paste it as the original font style, you can use the lasso tool 
to make the copy and paste it in place.