The OptimizerSens tool was removed in the 3.2 release because it was originally intended as a temporary work-around. It repurposed the optimizer code to generate a sensitivity image from list-mode data. It became obsolete once the castor-norm toolkit was integrated into CASToR. The doxygen is not up to date, indeed.
castor-norm generates a normalization list-mode file using a direct normalization approach. It requires as input the CASToR histogram datafile corresponding to a normalization scan (basically the datafile you provided when using the SENS optimizer) and an image of the normalization phantom (typically an annular phantom, but it depends on your geometry). This normalization file must then be provided to castor-recon with the -norm option.
As with the SENS optimizer, a large number of coincidences per LOR is required to obtain reliable normalization estimates. The normalization datafile can also become quite large for systems with a relatively large number of detectors like yours.
If you still want to use the optimizerSens, you can find the files here packed with the v3.1.1
You could find more details about castor-norm by using the -h option, or in the following discussions:
(Note that the GATE conversion tools are not yet available for GATEv10, but from your message I assume you developed you own tools)