Great suggestion @Kim_Theriault. I have the same need.
One way of doing this is to do this following workaround:
- Create a private Project called “Notes”
- Add a custom field (text) called “my note” but do not add it to the company library
- If you want to add a private note to a task. add the task to your “Notes” project and the new custom field will appear. According to me only you will see this custom field.
Hope this helps. If you want I can make a short video on how to do this setup.