Apple Books (iPhone): Read PDFs in Landscape mode

Until about a week ago, I was able to read PDFs in the Books app on my iPhone X (iOS 16.5) in landscape mode -- this permits zooming enough so that the text is legible, without needing to constantly scroll horizontally.

Now, I cannot; I even enabled the on-screen AssistiveTouch, which lets you pick a specific screen orientation, but the Books just ignores it.

Please tell me that this was an oversight and not the new normal -- portrait mode is a nightmare, and epubs aren't really viable for books with a lot of tables and diagrams.

Thanks!