> How does choosing your book’s font and margins apply to freedom of speech?

The fonts and margins dont communicate anything by themselves. There is a book that communicates ideas/opinions and that is what's protected by the first amendment. If someone found a font that exploits the brains reward mechanism and causes all sorts of mental health problems perhaps that should be regulated too.

Infinite scroll doesn't communicate anything by itself, it is purely a revenue maximizing feature that, as it turns out, has negative effects for people. There is no underlying idea or opinion here that Meta is communicating that should be protected by free speech.