This report was issued recently by Colorado Common Cause.
Short summary: VBM elections can and do increase turnout (and relative turnout) among Latinos – at least in off-year elections.
But Colorado’s practice of declaring voters “inactive” for missing any single election disproportionately impacts communities with lower overall voting rates (of course) and that this is especially a problem in mail elections.
To toot my own horn: as I’ve argued in recent papers published in PS and in a forthcoming Brookings volume, elections are complex. The parts are intertwined. Just changing one gear, like allowing voting by mail, is very likely going to affect, and be affected by, other parts of the election machinery (such as how quickly you move people to the inactive rolls).