Around November 2023, American Express Australia changed the format of the PDF statements by not embedding the font. This made rendering of the page virtually unreadable on macOS. Inspecting the PDF shows that it uses two fonts from the Bento Sans family.
To make the pages render properly, the fonts can be downloaded from sites like https://fontsgeek.com/tagged/styles/bentonsans
After installing the fonts, restart your PDF reader and all should be good.