Samsung already released the Android 11 based One UI 3.0 updates to Galaxy S20 and Galaxy Note20 series. And today, an Admin officially announced the One UI 3.0 beta updates for Galaxy M31 on Samsung Community forums.
For now, One UI 3.0 beta update is only available in India. You have to join One UI 3.0 beta program by clicking on the registration banner in the Samsung Members app. After registration you will get the beta update via >software update on Settings.