A lot less people actually looking for work. Some extra died. Some decided to retire early. Some are just flipping jobs looking for greener pastures.
https://www.bls.gov/opub/mlr/2022/article/us-labor-market-shows-improvement-in-2021-but-the-covid-19-pandemic-continues-to-weigh-on-the-economy.htm
Total employment, as measured by the Current Population Survey (CPS), rose by 5.4 million over the year, to 155.2 million, which was well below its prepandemic level of 158.5 million in the fourth quarter of 2019.5