Screen orientation under WSA

I started experimenting with WSA today because I want to use Moon+ reader on my Microsoft Surface device, and it doesn't have a native Windows version. The app seems to work so far, but the app's screen rotation button simply doesn't function. When tapped, it displays an animation, but does not turn the orientation. When long-tapped, it displays a context menu with multiple choices, some using a static orientation and some sensor-based. When choosing a sensor-based one, I get the message that I have to enable automatic screen rotation (presumably from the Android settings menu), and when choosing a static one, nothing happens. I want to use a static portrait orientation - this is very important to me, because I want to display full A4 pages on the screen, and read them no matter how I turn the tablet. But I don't know why it doesn't work, and as this is running on WSA, I can't even try changing the Android-internal settings for screen orientation. What can I do so my app will start turning the screen as it's supposed to?