From 2008 through 2018, the General Social Survey surveyed 814 non-citizens living in the US. Eighteen of those 814, or 2.2%, reported voting in a US presidential election during that time. The number who would have been legally permitted to have done so would of course be zero.
Maybe it’s transcription error, maybe it’s respondent confusion over voting in local or state contests in jurisdictions that do not require US citizenship to participate in lower level elections, maybe it’s trolls yanking interviewers’ chains–or maybe non-citizen voter fraud is a real thing.
GSS variables used: USCITZN(2), YEAR(2008-2018), PRES04, PRES08, PRES12, PRES16