Data between August and November 3rd, a little more than a week prior to the launch of the M1 Mac mini shows Apple at around 15% share in the desktop market, behind Lenovo Japan. However, following the launch of the new Mac mini on November 17th, Apple charged forward to a whopping 27.1% market share, a 14.4% increase from just the start of the month.
https://appleterm.com/2020/11/30/m1-mac-mini-desktop-market-share-japan/