hi there;
Hmmm… I was able to use LibreOffice on my mac to generate a PDF/A formatted PDF, which solved this problem. Same computer, same version of OSX (11.1). Details in PDF fails Ingram validation with error about "PDF CONTAINS ICC COLOR PROFILES" and needing PDF/X-1a:2001.
Regardless of problems might exist with Apple, I note that LibreOffice can do this on OSX, hence my post here asking if Scrivener could do whatever LibreOffice does. Only when doing “Compile->Print” so as to not disrupt people who want PDFs with layers, color etc.
(LibreOffice are open source too, so the code is visible, which might help?)
John.