The most imbalanced group in hiring were Asians, representing around 5% of the population but around 40% of the chart in that article. From my anecdotal experience with DEI programs, they generally don't target or encourage hiring Asians over black/Hispanic people. If we are purely talking about discrimination against white people, it's much more likely that an Indian or Chinese person is replacing a white person, not a "DEI hire" black person.

but Whites with a professional degree are much more likely to already be employed, or be able to retire (creating opening for new hires)

no it’s because the study is measuring net changes and most retiring professional degree workers are white