What critical design capability did the uncrewed Starliner return successfully demonstrate?

Autonomous operation during undocking, deorbit burn, and reentry.

A key feature of the Starliner's design that was validated by the uncrewed return was its capacity for autonomous flight during the critical return sequence. This means the spacecraft is engineered to manage essential phases—such as undocking from the ISS, executing the deorbit burn, and navigating atmospheric reentry—relying solely on its internal flight control software without immediate human oversight from the crew or ground control intervention during these segments. This successful autonomous execution, especially following the anomalies experienced earlier, provided crucial data validating the health of the guidance, navigation, and control systems under post-stress conditions.