In what year did the UK officially leave the European Union?

The United Kingdom officially left the European Union on January 31, 2020. This date marked the conclusion of a lengthy negotiation process that began with the referendum in June 2016, where the majority of voters opted for leaving the EU. The transition period that followed the official departure lasted until December 31, 2020, while the UK and the EU worked on establishing their future relationship. This context clarifies the significance of 2020 as the actual year of departure, despite earlier discussions and events leading up to it.