Samsung is yet to detail the March 2019 security patch but the recently launched Galaxy M20 has just received a new update that brings this security improvement on the air.
The latest update for Galaxy M20 brings March 2019 security patch along with Amazon shopping application (as bloatware), as well as Camera improvement, device stability and bug fixes for better performance.
The Galaxy M20 receiving this update with build version - M205FDDU1ASB4 and the size of this update is 367.94MB. Although this update is for Indian models, while there's no confirmation on the variants of this phone outside the country.
If you want to check this update manually, head towards Settings > Software updates.