It seems that the Switch may have had the biggest March of all time based on VGC historical numbers? Does March count as 4 or 5 weeks here?
The Hardware-To-Date chart is not displaying numbers for Wii and NSW at the moment (other systems show up and the graph for those two shows up). But I think this current March is ahead of the DS's best March.
Switch also took the November record back in Nov 2019 for VGC numbers.