Well no, a new decade has not begun, no matter how much some media insist on it: 2020 is the last year of the second decade of the 21st century, which, by the way, began on January 1, 2001. In the case of decades, the confusion has a lot to do with it. see with the widespread custom of naming them by the tens figures, as in the well-known expression "the roaring twenties", which seems to include all the years that have a 2 in that place, from 1920 to 1929 both inclusive.
