Money supply growth fell out of favour as a policy target in the 1980s because the relationship between money and nominal spending proved unstable, mostly because velocity-of-money moves. The 2020 to 2023 episode revived interest, since the fastest M2 growth on record was followed by the fastest inflation in forty years.
M2 shrinking is unusual and worth noting: it happened during quantitative-tightening as deposits migrated into money market funds and bank credit contracted. The link to inflation is real but loose, and the lag is long enough to be nearly untradeable.
Example: M2 grows 25% in a year while real output capacity grows 2%. If velocity-of-money were stable, the identity would imply roughly 23% nominal spending growth; velocity collapsed instead, so the inflation arrived later and smaller.
Related: velocity-of-money, quantitative-easing, quantitative-tightening, bank-reserves, inflation-expectations