Will preface this by saying I have absolutely no expertise on this subject, since I’m just a first-round PhD applicant!
It’s certainly not unheard of to pursue a literature MA/PhD if you’ve got a STEM undergraduate degree— many of the current graduate students’ profiles I looked up whilst researching programmes listed STEM backgrounds. However, and sorry if this is unhelpful, I’m a bit confused on what your academic goals are, and what you regard as being a ‘literary scholar’. Also, you mention creative writing as a previous passion— have you considered an MFA, or are you definitely more interested in studying, rather than writing literature now? Sorry, I know you’ve already clearly stated your interest in critical theory and contemporary American lit, but since you seem to have a talent and passion for creative writing, I’m wondering if that’s a track worth considering/ one that would fit with your interests and goals best.