Samsung has started distributing One UI 4.0 Beta 2 to the Galaxy S21, Galaxy S21 Plus and the Galaxy S21 Ultra. The new beta build is available in several countries, including India and the US. One UI 4.0 Beta 2 adds Google's Material You theming options, among other changes from the first beta.
https://www.notebookcheck.net/One-UI-4-0-Beta-2-rolls-out-to-the-Samsung-Galaxy-S21-Galaxy-S21-Plus-and-Galaxy-S21-Ultra-with-Material-You-theming-options.569466.0.html