Today, official Beta Operation Manager at South Korea accidentally posted banner for Beta testing for One UI 4.0 version. Later, the manager deleted the poster from the account, which creates lots of confusion in between users. It could be mistake made by Beta Operation Manager and he posted it online. The poster claimed that One UI 4.0 beta or Android 12 beta for Galaxy S21, Galaxy S21+ & Galaxy S21 Ultra will start soon. The banner has taken down after few minutes for some reason, but the message was spread everywhere.
Now to make it clear, the official team member has answered to users about actual release date for beta testing. As per the official team, the Galaxy S21, Galaxy S21+ & Galaxy S21 Ultra will get One UI 4.0 beta version in September & October. And the previous Galaxy S20, Galaxy S20+ & Galaxy S20 Ultra will start to getting in October. That means, the beta version for Galaxy S21 could start in the last week of September in South Korea , and it will reach to other major countries in early October.
Here is the official answer from official team member of Samsung in South Korea. It is the translation of the answer given in South Korean language.
However, in the case of Android 12 of the Galaxy s21 model, it is confirmed that preparations are in progress with the Android 12 beta starting around September and October in the second half of the 21st year. We ask for your understanding that it is difficult to provide accurate information because the support plan or official information on the supported terminal has not been announced.