Thermal scattering behaves a little bit differently from incident neutron data in this respect. ENDF thermal scattering files have data listed for specific temperatures and there’s no straightforward way to “Doppler broaden” them to other temperatures. Instead, what you’ve have to do is run LEAPR (or an equivalent code) to generate a new ENDF file with data at the temperatures you need. I know some organizations do this when the ENDF file provided in the main library only has data on a very coarse temperature grid. If you have access to the underlying phonon frequency spectra, they can be interpolated to the desired temperatures and fed through LEAPR to give a new ENDF file.
In your particular case, when you run from_njoy with no temperatures listed, it will use all available temperatures in the ENDF file. This means that whatever data you are processing, they only have data listed at room temperature unfortunately.