There must be data for underemployment
It is trending up but is still lower than pretty much any time since the 2008 recession: https://unemploymentdata.com/current-u6-unemployment-rate/
Millennials have spent most of their careers systematically underemployed.
https://dol.ny.gov/system/files/documents/2021/03/overview-o...
I recommend "Applied Panel Data Analysis for Economic and Social Surveys" by Hans-Jürgen Andreß, Katrin Golsch, Alexander W. Schmidt, if you would like to learn more.