Sorry, my previous reply referred to distributions from a Roth IRA, not from a traditional IRA.
Also, I had assumed that you were referring to the code in box 7 of the Form 1099-R. I know nothing about Michigan codes, so disregard everything that I have said previously in reply to your question. You might consider asking the question again in a new thread so that it shows up as unanswered.
Still, it looks like Michigan code C would apply to your Roth conversion. I suggest looking at page 19 of the instructions for Form MI-1040:
https://www.michigan.gov/taxes/-/media/Project/Websites/taxes/Forms/IIT/TY2024/MI-1040-Instructions....
