Where twenty percent comes from
The twenty percent figure is a convention, not a requirement. It comes from an era when that was the standard expectation, and from the fact that avoiding mortgage insurance is a real financial benefit. It is a sensible goal — it is just not the entry fee.
Several loan programs are designed with lower down payments in mind, and some eligible borrowers can buy with nothing down at all. Which of those applies to you depends on the program and on your situation.