The #1 on M Countdown on 2020-03-12 was “So What” by Loona — win No. 1 for the song and career win No. 1 for Loona (No. 1 on this show).
“So What” has 1 music show wins in total: 2020-03-12 M Countdown. Loona had 1 wins in 2020 up to this date, and this was the artist's first win on M Countdown. The previous week's M Countdown #1 was “On” by BTS. Episode data comes from broadcasters' published results (Wikipedia lists, CC BY-SA) and is recounted daily.