Georgia's former (pre-pandemic) system for absentee ballots was very similar. I used it when I was away at college because I had no interest in voting in NJ.
You applied by affidavit with proof of identity. I went in in person when I was home on vacation, but I believe they had a system for overseas military and shut-ins.
I have voted in every election since 1974, including by absentee. The very first time I ever had any trouble was 2020. Because of the pandemic I applied for a mail-in ballot "just in case". It never arrived, and when I went to vote in person I was told I had already voted. Nope. Had to swear out an affidavit - and the elections supervisor said they would compare the signature w/ the mail-in ballot. But I don't see how they had any prayer of finding it. At best I cancelled out the fraudulent vote.
You’re absolutely right, for years and years I’ve always called it absentee ballots, for some reason the media and some Republicans started referring it to as Mail In ballots, the two are completely different.
I had a heated debate with another Freeper who vehemently disagreed with me, I said Florida did not allow mail in voting, they allowed absentee voting and the two were very different, he vigorously disagreed, I’m not sure he ever got the difference.