\(\sqrt{\left(1-\sqrt{2020}\right)^2\cdot\left(\sqrt{2021-2\sqrt{2020}}\right)}\)
\(=\sqrt{\left(1-\sqrt{2020}\right)^2\cdot\sqrt{\left(1-\sqrt{2020}\right)^2}}\)
\(=\sqrt{\left(1-\sqrt{2020}\right)^2\cdot\left(1-\sqrt{2020}\right)}\)
\(=\sqrt{\left(1-\sqrt{2020}\right)^3}=\left(1-\sqrt{2020}\right)\sqrt{1-\sqrt{2020}}\)