I have one custom setting in our org which is not searchable, as verified by confirming that searchable = FALSE when viewing the object info via Workbench. Dozens of other custom settings in our org are searchable, and I can't see any significant difference (in visibility, settings type, etc.) which would explain the difference in behavior on this one.
One online article suggested that the option to allow the custom setting to be searchable would have been selected when the custom setting was built. However, I created this custom setting myself, and I don't remember making any such selection.
Another article suggested that enabling the org-level "Enable SOSL on custom settings" option (located in Classic under Data Management > Schema Settings) would do the trick. But I tried it and there was no change to this object.
Has anyone run into this before? Do you know how this custom setting could have gotten non-searchable in the first place, and any way we could make it searchable now?