About File name in a Tag Panel

Hi, Happy New Year to everyone!
I have a problem to set the field 'File nane' in the lateral tag panel.
Since it was not present as a field among the items, I added it myself.
But the entry does not appear in the field ...

This is what i did:
Right click on the tag panel, appears mp3tag option window, I select item 'tag panel' from the list on the left. In the center there is the list of fields visible in the tag panel. I click on the first button on the top right 'Add/Edit field'.
I fill in all the items and in the first, in 'Field' I select 'ORIGFILENAME' from the drop-down menu. But obviously it is wrong because once everything has been saved, it does not appear in the Tag Panel field.
I also tried to change the item from the drop down menu but nothing ever appears.
Can you help me?
Thanks a lot !

To address the filename, use the property name _FILENAME.
The tag panel field definitions do not accept any field (or property) name that starts with an underscore - these properties are usually read-only and in most cases not handled by MP3tag.

Thanks for the reply.
I tried to change but nothing happened.
Could you explain me better? What should I write to direct it right on the filename?

You cannot edit the filename in the tag panel.
You cannot add _FILENAME to any item in the tag panel.
This is not only valid for _FILENAME but any property that starts with an underscore _, e.g. _LENGTH, _PATH, _DIRECTORY, _TAG

Ah ok, thanks.
But, then, why do I see the Directory field?

The directory field is one that has been in the tag panel for a long time and you will see that it does not behave the way the other fields do:
It has its own history of entries.
It shows data even though no file is selected.
Enter a new path in the field and that folder will be read and become the working directory.
For all other properties with an underscore: don't ask "why", accept it as the way it is: they cannot be added to the tag panel as fields.

Too bad, it would have been comfortable.
But anyway if that's the case ... we accept it.