The correct answer to this open question is the following.
The three myths and fallacies that I heard in my family or community are the following.
1.- If you rinse with warm salt water, you are going to kill the coronavirus.
2.- Watch out! Cholesterol is bad for your health.
3.- Eat chocolate. It is an aphrodisiac.
They say that one lie retold many times became a truth. And many times it is true. The problem is that people do not like to inquiry, ask questions, go get the proper sources to confirm what they hear or read on social media. That is the problem. That is why myths have a life on their own.
People have to check reliable sources to learn, or to confirm what they hear. One of the best sources is your medical doctor. He is an exért and spent many years in college and a couple of more years in his specialization. Go ask them.