Hello, how are you? I am using the latest apex/ords for my application.
Well the title says it all. As well as the following screenshots.
Page Item Substitutions Strings do not work on "Page Header Text" Fields of Interactive Report/Grid settings. However System Variables do work.
The same behavior applies to "Page Footer Text" and "Supplemental Text" Fields.
(Please not that P5_NEW just has some static text)

