Yup, proving things like protected classes usually requires either a super stupid manager (who puts it in writing, or says it in front of coworkers who are willing to testify for you), or proving a sustained pattern of behavior. Because a manager can just go “I didn’t like their vibes” and get away with it most of the time. Because disproving a soft subjective thing like “bad vibes” is basically impossible. Instead, you need to prove a pattern of behavior, like all of their “bad vibes” firings within the past two years have been black people. But getting access to that kind of thing will require a subpoena and lots of investigative work.