One (of many) plausible scenarios:

Robin DiAngelo is talking about empathy. She asks people to put them self in the sues of a minority, knowing how boring it is, she puts the words “Try to be less white” on the slide in an attempt to humor.

Another possibility:

She has been working up the argument that whiteness is a social construct, and in this context, “being white” is the same as “being socially constructed to perceive your self as superior”. In that context asking people “to be less white” is not a judgement on the color of the skin.

It may be something entirely different though, point is it is not hard to come up with a context where these slides are not criticizing the color of people’s skin.