List fields are not selectable from the field selector list on list fields. Rather than any field that references the table of your List references being available, only reference fields are available.
Steps to Reproduce
Add a new Table name field (Table Test) to the Incident table.
Add a new Glide List field (List Test) to the Incident table, referencing sys_user.
Edit the Dictionary entry for List Test. Set Dependent Field to Table Name, and add the attribute: field_list_selector=sys_user.
On the Incident form, set Table Test to Knowledge [kb_knowledge].
Click the Lock icon for List Test, and click Select Fields.
Expand the knowledge base.
Note that Managers doesn't appear as an available option even though this field references sys_user. Other reference fields that are not Glide Lists display as expected.
After carefully considering the severity and frequency of the issue, and risk of attempting a fix, it has been decided not to address this issue. We do not make this decision lightly, and we apologize for any inconvenience. If you have any questions regarding this problem, contact ServiceNow Customer Support.
Related Problem: PRB1116366