From the Introduction: "In 2020, the COVID-19 [coronavirus disease 2019] pandemic caused disruptions in the daily lives of people in the United States and around the world. Policies meant to slow the spread of the coronavirus (such as community-level stay-at-home orders) forced organizations to change how they operate. The pandemic complicated the operations of the American Community Survey (ACS) in a variety of ways. Throughout the year, the survey adapted to the circumstances by changing operations to protect the health and safety of Census Bureau staff and the public. [...] This report describes the elements of the survey that were affected by the pandemic. The information is presented in order of survey processes."
U.S. Census Bureau: https://www.census.gov/