It's not the 21st.
The first day of spring is Monday, March 20, 2023, at 5:24 p.m. EDT. For those of us in the Northern Hemisphere, this was marked by the arrival of the Vernal Equinox (otherwise known as the “First Point of Aries“).
https://www.farmersalmanac.com/spring-equinox-first-day-spring