The chart in the image was reproduced by the Washington Post from a 2009 study by I C McManus

The Post article makes a similar claim to the one in the screenshot

McManus theorizes that the late-Victorian dive in left-handedness reflects stigma against southpaws

https://archive.ph/y543P

But he actually said this is unlikely

One possibility, extensively discussed in the handedness literature, is that left-handers die earlier […] An alternative explanation of the lower rate of left-handedness suggests that the elderly are more likely, because of social pressure, either to have been forced to shift from writing with the left hand to writing with the right hand, or they prefer to call themselves right-handed, because of a taboo against left-handedness. Both this and the differential mortality explanation become unlikely when one looks at the entire Gilbert and Wysocki database […] The best account of the Gilbert and Wysocki data is that it directly reflects the actual rate of left-handedness in the population

(pdf): https://jhanley.biostat.mcgill.ca/bios601/CandHchapter06/HistoryGeographyHumanHandedness.pdf