I thought it started in the Frankfurt School.
Yes- the Frankfurt School social theorists developed the underlying thinking. An important example is Herbert Marcuse’s essay “Repressive Tolerance”.
Juergen Habermas, a student of Adorno, was not part of the Frankfurt School per se, but he coined the term “critical theory” and much of the perspective. But he didn’t go so far as to say that structural injustice was insurmountable or a subconscious consequence of “privilege”.
This last idea was suggested by Michel Foucault, who wasn’t part of the Frankfurt School, although he was influenced by it. He wasn’t a Marxian, and later in life he sounded more like the (conservative) novelist Michel Houellebecq than anyone in the Frankfurt School.
Legal Scholarship was transformed first (also with influence from John Rawls), then the humanities, then social sciences, and then the physical sciences.
Even before critical theory penetrated these disciplines, grievance studies emerged (1970s) as “interdisciplinary” fields, e.g. African-American Studies or Women’s Studies.
The contemporary CRT celebrities like Derrick Bell or Nikole Hannah-Jones won’t acknowledge the Frankfurt School
Every “innovation” in education over the past 50 years has come from the radical left.