Once again a little bit of research changes the view: Savings are now part of M1

“Before April 24, 2020, savings accounts were not part of M1. Limitations in the number of transfers from savings deposits made savings accounts less liquid than M1. M1 consisted of currency, demand deposits, and other highly liquid accounts called “other checkable deposits” (OCDs). An example of OCDs are the demand deposits at thrifts.

But the limitation on the number of these transfers was lifted on April 24 as an amendment to Regulation D, which specifies how banks must classify deposit accounts. Savings deposits are now just as liquid and convenient as currency, demand deposits, and OCDs. To reflect this fact, savings deposits are now included in M1.”

So starting in May 2020 all savings accounts were added into M1, thus the big rise.