I only see the information of a category in the chronos if the field is selected in the Chronos form.
The COMP$ADDRESS.CITY field for instance, I added it as a test
Only then I see the field information in the chronos.
If I remove the field again from the form, it is no longer visible.
Double check if the field you don't want to share with all users is part of the form? If so, remove it.
There is also security on the change history. If I don't have rights, I don't see the category change
When I have the rights, I do see the change. So, that works pretty well out of the box.
Tested with Efficy 11.1