Workforce is a new resource added in Anno 2205. Unlike previous anno games, one of the requirements for a building to run is a workforce. This means that having islands/sectors without any population will be extremely challenging compared to the previous titles (possible with drone hive modules).
The workforce is dependent on your population/employees. In the early stages of the game each person will count towards the workforce, but as the housing buildings get promoted to higher levels, the percentage of the population in said building contributing to the workforce decreases.