Google Workspace users can now use custom fonts in Google Forms. There are size limits for each section, but you can change the font in the: Google Form Title, Test Questions, Descriptions, Answers, and Section Titles. See below for font size limitations.
Google Form Size Limits
For a step by step instructions on how to change the font, add additional fonts, see the tutorial above.
You can use any of the Google Fonts, including the additional fonts in the (More Fonts section). Google is also releasing Rich Text Format in Google Forms which should be available in the coming weeks.