Try KOReader, it can rotate itself any way you want. I also use a plugin for it which automatically rotates depending on the aspect ratio of the page. Can also change the font size on the fly, zoom in and out and it’s available as Flatpak on the Deck.

The UI is made for e-ink displays so don’t expect a beautiful UI with it but the reader is one of the best. I recommend reading the manual which opens on first start, it’s mostly controlled by gestures.