Organizing an iftar for eligible (needy) people, where food is laid out onto a suffrah or table, does not fulfill the obligation of Sadaqah al Fitr. This is because it is mandatory to give the recipient full ownership of the item or amount given as Sadaqah al Fitr, so that they can use or spend it as they wish. In the case of iftar being laid out on a suffrah or table, people can eat whatever they desire from the food in front of them, but they are typically not permitted to take away the leftover food. Therefore, they do not gain full ownership of the food. This is termed as "ibahat" in Arabic.
Additionally, when organising an iftar in this way, it is difficult to determine whether the people being fed are eligible for sadaqah al fitr according to Shariah or not. Because of this, and the reason stated above, organising an iftar does not fulfill the obligation of Sadaqah al Fitr.
The correct way of doing this is to distribute packets of food to eligible individuals. This ensures that the recipients gain full ownership of the food, which meets the criteria for Sadaqah al Fitr stated above.