Found a paper that is pretty depressing.

...this study provides evidence of the negative influence of over-education on wages (i.e., the over-education wage penalty) once potential sources of bias are adequately considered. While the current analysis is focused on one country, South Korea, its results might be relevant for many other countries that have experienced a rapid expansion in the supply of DHs over recent years...

Park, K. (2022). Doctoral Education, Job Mismatch, and Wage Consequences in South Korea: A Propensity Score Matching Approach. Journal of Asian and African Studies, 57(7), 1325–1342. https://doi.org/10.1177/00219096211052978