Although the Ngram chart in Mitch's answer provides a heartening view of the decline of learnings in published texts included in the Google Books database (from the bad old days of the 1950s through about 2008), a more up-to-date look at the Ngram chart for learnings (starting, as Mitch's chart does, in 1910 but continuing through 2019) shows that the word has been on the upswing since about 1990 and that it has really begun to pick up steam in the past ten years:

This may reflect, in part, the vogue that learnings has enjoyed in business-speak in recent years, as MBAs—the same people who gave us "If you have to pose the ask, you can't afford the spend"—have embraced the notion that teachings beget learnings. I spend a lot of time editing business articles, and I can tell you that the enthusiasm for learnings in that sector shows no sign of abating. We're still in the early stages of a second wave at this point, but a wave it appears to be.