evenin'
Classified executive orders existed and were used by at least President Clinton. Probably a safe bet they were used further back.
FOIA Update: Executive Order 12,958–Classified National Security Information
Sunday, January 1, 1995
https://www.justice.gov/oip/blog/foia-update-executive-order-12958-classified-national-security-information
And here's the Federal register showing the actual list for President Clinton.
This is just one example.
gap in the numbering from the federal register
https://www.federalregister.gov/presidential-documents/executive-orders