The efficiency calculation is possible only if you use a non-isothermal heat transfer model with compressible fluids. For devices that involve a very small enthalpy change (or temperature change), ensuring that your material definition uses a small reference enthalpy might help to avoid inaccuracies.

The boundary lists enable only single boundary conditions of type Inlet or Outlet.

Multiple component efficiencies cannot be directly monitored using the existing interface. The best approach is to activate the field output and use the expression monitor option to monitor the efficiency change across the given component.

Total to Total and Total to Static efficiency values cannot be evaluated at the same time. You must select one mode or the other.