There’s no sign of the rumored Pro Mode, but the update does have some other goodies.
macOS 10.15.3:
- Optimizes gamma handling of low gray levels on Pro Display XDR for SDR workflows when using macOS
- Improves multi-stream video editing performance for HEVC and H.264 encoded 4K video on the 16-inch MacBook Pro (2019)
It is available now via Software Update in System Preferences.