Open Status set from Edit applicant Status set configuration and check for particular status , the required option is not greyed out.
SuccessFactors- Bizx Recruiting
The status must have checked the option "Collect Comments if this status is skipped".
uncheck this option and then you can make the status as a required field.
The option checked itself says that you can skip the status , the reason why the required section is greyed out.
Applicant status, Required status, edit applicant status , KBA , LOD-SF-RCM-ADM , Admin Center, RBP, Permissions and Settings , Problem