It was removed because it was a really exotic feature not many people used. You can still perform the analysis of course, you just need to script it, either from the Workflow Builder or, almost easier, directly by hand. Of course it was a lot more fun when you could just click, because now you need to run multiple scripts just to check how many finite transmission channels you have, and then get the eigenstate, and drag it into the Viewer...
device_configuration = nlread("myfile.hdf5", DeviceConfiguration)[-1]
energy = 0.0*eV
eigenvalues = TransmissionEigenvalues(device_configuration, energy)
nlprint(eigenvalues)
Then second run
device_configuration = nlread("myfile.hdf5", DeviceConfiguration)[-1]
# Same energy as before
energy = 0.0*eV
# List here the interesting quantum numbers
quantum_numbers = [0,1,2]
for quantum_number in quantum_number:
eigenstate = TransmissionEigenstate(device_configuration, energy, quantum_number=quantum_number)
nlsave('myfile.hdf5',eigenstate)