Alongside the fourth macOS Ventura 13.3 beta that came out today, Apple has provided a new beta of the 16.4 firmware that's designed for the Studio Display. The beta comes a week after the third Studio Display 16.4 beta.
All Studio Display models are able to receive over-the-air firmware updates, but this firmware update is limited to Macs that are running the macOS Ventura 13.3 beta at the current time. Studio Display owners running macOS Ventura 13.3 can go to System Settings > Software Update to install the firmware.
Apple has not provided details on what's included in the firmware update.
Source: Macrumors