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Onenote differs from most note managers by writing on several blocks of text on an infinite canvas, instead of a single block of text. This has advantages, especially on large screens, but it makes reading on the mobile a horrible experience.
It would be good if from mobile apps we can switch to reading mode, which adjusts the text block to the device width and the font size is what is adjusted when zooming (not the text block).
Regarding those pages where the user has several blocks of text in different places on the canvas, I can think of two options:
1) ban the mobile reading mode on those pages.
2) or better yet, sort the text blocks one below the other.
Anssi Niemi commented
The app is more aggressive in reflowing text than it needs to be.