Currently, CDMPrivateThunder::supportedRobustnesses() is implemented to set the supported robustness levels to "SW_SECURE_DECODE" and "SW_SECURE_CRYPTO", corresponding to Widevine security level L3 (lower). Platforms that have HW support to comply with Widevine security level L1 (higher) will not have that capability propagated to the upper levels.
Initial thought would be to extend opencdm API to return actual capabilities from the platform and set the robustness levels accordingly, but this requires some thought and review to identify the appropriate solution.