This was one of the issues in 2020. If a person voted in person, but a mail in ballot was received that mail in ballot was just rejected. Lots of politicians from one party were adamant about telling people who voted by mail to show up in person as well because the mail in ballots may not arrive in time. So there were millions of people with double votes where the mail in was auto-rejected. When analyst tried to nail down exact numbers or to audit specific instance it turns out the rejections we're not logged. The best they could do was determine, in some states, the number of people who requested absentee, but voted in person.

When contacting these people many claimed they did not request or receive the mail in ballot.

In states like California where everyone was mailed a ballot, a voters who mailed a ballot but weren’t sure if it was counted were asked to vote in person using a provisional ballot.

We do not know that this isn't an issue.

You have described one particular case that doesn't involve fraud or bad actors. That is called a strawman argument.

I don’t follow

Unless you’re one of the states that doesn’t have in person voting, like Washington.

It is of course possible to vote at a physical polling location in Washington state

Is it? Having lived in Washington since the age of 4 and voted in virtually every election since I turned 18, I’m not aware of this.