So “ARTISTSORT” is the value? (is what I have to write down in the Value field?). I do not think so, artist value is a weird code “$metasep(artist,\)” not “ARTIST”.
& what about the field? Artist field is “%artist%” so probably Artist Sort field is “%artistsort%”?
BTW I don’t know how to get to the table you shared Motley Tag Field Mappings Table – Mp3tag Documentation
When I read the Customization of Tag Panel and File List & Format Strings and Available Placeholders the link you shared was not mentioned.
Furthermore, do not understand for what is this mapping table useful, it does not seem it says which data write down in the Value & Field field.
I just say this to let you know that for somebbody who is beginning is hard to uderstand & follow you.