Yes, the main fear is non-citizens voting. A secondary fear is people in cities voting multiple times.
Having lived in NYC, that fear seems absurd to me. I live in a state where people supposedly get “bussed in” to vote, which is nonsense.
Still, we have 11 million people in the country who should not be voting in elections. That’s just illegal people. Those here legally, with a green card or visa, can’t vote either.
Anyone in the country illegally would be taking a huge risk by voting.