Samsung has announced on its community forums that it will be releasing the One UI 4 beta in September, although Samsung didn't mention a specific date.
According to the announcement, the Android 12 based One UI 4 will be available for Galaxy S21 series users first once it goes live. Samsung's One UI 4 will bring changes to the platform such as visual enhancements, new app icons, and accent colors to match the theme of the device. Samsung will also tighten the operating system's security using the Samsung Knox with additional under-the-hood improvements.
Meanwhile, Google's Android 12 is in the beta stage too and will be released to the general public later this year.