:EXPORT_FILE_NAME: (format-time-string "%Y-%m-%d") Project Status.html
Yes, you cannot do that (How would Org know that you do not want to name your file literally like that? :)).
Also you do not need to (should not?) provide the file extension there.. the correct extension is added based on the exporter you use.
That said, I quickly tested this out, and it works:
(defun modi/org-advice-prefix-export-file-name-with-date (orig-fun &rest args)
"Prefix the output file name with current date."
(let* ((date-format "%Y-%m-%d") ;Customize this variable as you like
(date-file-separator "-") ;Customize this variable as you like
(orig-output-file-name (apply orig-fun args))
(orig-output-dir (file-name-directory orig-output-file-name))
(orig-output-just-file-name (file-name-nondirectory orig-output-file-name))
(date (format-time-string date-format (current-time))))
(concat orig-output-dir date date-file-separator orig-output-just-file-name)))
(advice-add 'org-export-output-file-name :around #'modi/org-advice-prefix-export-file-name-with-date)
;; (advice-remove 'org-export-output-file-name #'modi/org-advice-prefix-export-file-name-with-date)
After evaluating the above, current date will be prefixed to the exported file name, whether you export the whole file or just a subtree.