What's the 'Sharpiegate' conspiracy theory alleging voter fraud in US election?

Social media posts claimed that some votes cast for US President Donald Trump were not counted in Arizona because voters used Sharpie pen provided to them by election officials. Similar claims have circulated in other states including Michigan. Refuting the allegations, officials said, "Sharpies don't impact tabulation, and we encourage them...because of how fast the ink dries."