The Heritage Foundation is a pretty reliable group even if they are Conservates. These statistics are not meant to imply that the number convicted is close to the number of crimes, any more than the number of tickets given for running stop signs is close to the number of violations.
However, when the claims of violations are in the hundreds of thousands and millions with only a handful convictions, it is a very good assumption that those claims are grossly exaggerated.
In the 2020 presidential election there were 5,500 irregularities reported with less than 500 being actually illegal voting that could be charged as a criminal offense. Of that 500, 32 were illegal aliens charged and the the number convicted was 16. Keep in mind there were 155 million people that voted. Even if ever reported incident of any kind was an illegal immigrant voter that would be only .00035% of the voters. Remember Trump was claiming tens of millions of alien votes.