If this were British Columbia, before you vote you must make a declaration that you are eligible and did not vote already.

If you voted earlier/somewhere else, you could choose to show up at any polling place later, as long as you do not make the false declaration to receive your second ballot, you will not have committed fraud. The election person can be like, oh the digital record shows you voted already, and you can walk out. In remote areas, the paper voter roll of local voters will show whether they know you voted or not but other paper locations will not (if your polling location was way out in the sticks and you went to another rural place to vote). Mail ins are much the same, your name and signature on the declaration is the same thing as the verbal affirmation.

I know Trump’s supporters are bad at logic, but this should show that these processes stop enough voter fraud to the point that you it’s not really they need to get all worked up about.