https://wccftech.com/apples-studio-display-with-a13-bionic-chip-runs-full-version-of-ios-15-4/

Apple recently launched the new Mac Studio and a Studio Display at its Spring event. If you have bought the latest machine and display from Apple, you must be aware of its capabilities. While the new Studio Display does not feature mini-LED technology, Apple made sure that users get the most in a more affordable package. Apple's Studio Display features an A13 Bionic chip, the same processor that powers the iPhone 11 series. It has now been discovered that the Studio Display runs a full version of iOS 15.4.

John Gruber from Daring Fireball highlights that Apple's Studio Display is running a full version of iOS 15.4. You can see the display's software under "Graphics/Displays." You can see that it is running version 15.4 with a build number of 19E241. The build number is the same as iOS 15.4 and iPadOS 15.4, indicating that Apple's new Studio Display runs a full version of iOS.