Thank you for adding more information. From your provided Google Document, I could know the font name. By this, I tested to change the font family to Google Sans for new created Google Document using Google Apps Script, I confirmed that the font can be changed to Google Sans. It seems that when the font name is directly set to the method of "setFontFamily", Google Sans can be used.
For this, I prepared the sample script to my blog
by adding the demonstration video. Could you please confirm it? If that was not the direction you expect, I apologize.