No, it is not a mistake
UEFA European Championship will start on June 11, 2021. Its official name is Euro 2020, and it is not a mistake.
As you know, Euro was moved from 2020 to 2021 due to Covid-19 coronavirus pandemic. At the same time, UEFA has been actively discussing the championship’s name.
Finally, UEFA Executive Committee decided that 2021 tournament will remain Euro 2020. UEFA said this will “keep the original vision of the tournament and serve to remember how the whole football family came together to respond to the extraordinary circumstances of the Covid-19 pandemic and the difficult times Europe, and the world, had to go through in 2020.”