Unkown Mixed bake mode in LightModeUtil.MapSettings() UnityEditor.DockArea:OnGUI() may be reported after installing Unity. Then I found two solutions to solve it successfully. You can learn from it.

1. Open Lighting->Setting under the window

Uncheck Realtime Lighting and Mixed Lighting

If you remove it and you still have it, re-tick it like I did, so that the error will be resolved.