Far too few.

Were it possible; employers might screen candidates on the results of a test of critical thinking, as opposed to a degree. However, this has been illegal since Griggs vs. Duke.

Wasn't the intent of Griggs v. Duke that the testing needed to apropos to the job? Meaning that "critical thinking" tests could be part of the job filter as long as they related to the job at hand?

Well, some places do leetcode... and then they ask if you have a degree.