Just for future reference, I've added this with v3.27:
[2024-07-04] NEW: added 'Copy as Text...' to File List context menu. (#65135)
This is possible with $columnValues(x,y) added in Mp3tag v3.36-beta.4:
NEW: added scripting functions
columnNames(x,y)andcolumnValues(x,y)to retrieve all names and values of File List columns.
You can also do things like:
$if($eql(%_counter%,1),$columnNames(,$char(9))$char(10),)$columnValues(,$char(9))
to copy a tab-separated textual representation of a File List column names and values.