I went back and found the study, half are secular and 9% are no longer Christian. Of those that went Protestant, 9% went mainline, 16% went Minority Protestant (congregations that are maybe more diverse protestant congregations racially) only 14% went White Evangelical Protestant which would be the overwhelming church affiliation of protestants here.
Thanks for the info. The former mainline Protestant denominations are dying, so it’s not surprising they don’t get many people moving in who are going from denom to another.