Because it's a secret ballot, vote returns by race/ethnicity, gender, or other demographics are only discoverable via survey. See my political survey guide for sources.
For a good explanation of the difficulties and complexities involved in collecting, cleaning, and interpreting precinct boundaries, see Redistricting Data Hub's explanation as well as Amos, B., Gerontakis, S. & McDonald, M. United States Precinct Boundaries and Statewide Partisan Election Results. Sci Data 11, 1173 (2024). https://doi.org/10.1038/s41597-024-04024-2. RDH also has useful articles on the processes and assumptions underlying (dis)aggregation in electoral analysis of data reported at differing geographies as well as vote allocation of (usually) county data to more granular geographies.