What version of Sametime are you running? I am not clear what you mean by “R9-R12”.
I see the “ST_PURGE_LOGS_OLDER_THAN” was discussed in v10.0 Sametime Community Server diagnostic files but this is an unsupported version. I don’t see this parameter mentioned in 11.6 or 12.0.x, which makes sense, as this likely does not apply.
@Fabrice_Papirnyk if you are running 12.02FP2 or 12.03 on a Windows non-containerized environment. the parameter ST_PURGE_LOGS_OLDER_THAN should still apply. If it does not work, please open a case with support. In a docker / Podman environment logging is very different than traditional Sametime logging.