Fore this is another option to save the "final" of the piece this would be a very useful, but the reason why I'm trying to use 'Export' is to transfer my individual layers to separate files, and the 'Export as new files' option isn't working as an alternative. So, how would I ungrey the 'Export' button?
"Export as new files" is the short command name in the organizer to write to disk new files from selected files (not layers), 'New' generally means something different than simple duplicates or unchanged copies: for instance resized, converted to new format or custom renamed. 'Export' in the organizer also implies that the newly created files are made available externally to any other organizing or editing software without being included in the catalog.
The 'Save as' editor command also combines the ability to create copies while converting and/or renaming.
Since you are wanting to create new files from layers, it would help to understand what is the point of needing new files for different layers. We could perhaps suggest other solutions than the good one provided by @Peru Bob .