Here is an article published in the highly respected Journal of Political Economy. Articles in this journal are peer reviewed by some of the top economists in the country. Although the article itself is gated (you can buy it for $30), the conclusion of the study is publicly available:
“We evaluate progress in the War on Poverty as President Lyndon B. Johnson defined it, which established a 20% baseline poverty rate and adopted an absolute standard. While the official poverty rate fell from 19.5% in 1963 to 10.5% in 2019, our absolute full-income poverty measure—which uses a fuller income measure and updates thresholds only for inflation—fell from 19.5% to 1.6%.”
Notice that this estimate is very similar to the estimate made by John Early, Phil Gramm, and Robert Ekelund in their book, The Myth of American inequality: How Government Biases Policy Debate.