What you see in that video is Fulton County election workers arranging, sorting, and verifying ballots.
It is what they did before and after people left.
They were not unsupervised. The person in the blue shirt is a monitor from the Republican Secretary of State’s office.
What happened is at 10pm, the Fulton County Board of Elections announced they were sending most everyone home. The Republicans decided that meant everyone was leaving, but that is not what was said. The Fulton County Board of Elections and the Secretary of State both attest that it was made clear they were sending most people home, not everyone home.
The Secretary of State’s monitor stayed to observe.
Nothing nefarious was seen.