The Samsung Galaxy S22 series received Android 13 (One UI 5) beta builds in the US. The One UI 5 beta releases for the Samsung Galaxy S21, Galaxy S21+ along with the Galaxy S21 Ultra are now available upon Android 13.0.
Reddit user u/DJStormXZ found the latest update to the GalaxyS21 subreddit.
As per the OP (original poster) The beta models are only available to the purchase of US-based models that are unlocked.
Another user also stated that they could download the beta version to T-Mobile phones.
I was unable to see the new card in my Samsung Members app because I owned a TMobile Samsung S21 ultra.
UK as well as Korean Samsung Galaxy S21 owners can download the beta update at the end of last month (India has been updated more recently) as well as the US beta build is somewhat newer version, and has building number G991UEU5ZVIA (for the S21). Redditors believe this to be Android 13 Beta 2.
If you reside located in the US and have a Samsung Galaxy S21 model, you can visit Samsung Members. Go to Samsung Members app and swipe through the banners at the top until you come across one that reads “One UX Beta program.”
Click on the banner to join to receive Android 13 beta prior to when it goes out to the general public. Be aware that an Galaxy S21 that is locked to a specific carrier might not be able use it.