That's interesting, so not related to iPadOS 26 then.
Unfortunately, I can't remember how long it has been like this, but I have been looking back through the now playing thread, and most people post screenshots in portrait mode (myself included), but you have posted a few portrait ones, including this one from 7th September, which predates iPadOS 26 (unless you were on the beta version).
The WiiM Home app was at version 3.3.4 back then, so this behaviour could have started with version 3.3.5 possibly?