It appears that UICollectionViewCompositionalLayout has issues with accessibility when using orthogonal scrolling sections. I recently updated a CollectionView in our app to use compositional layout / diffable data source and noticed that the accessibility inspector only reads the cells that are queued initially and doesn't scroll horizontally to trigger reuse and reach the end of the list. Instead, it reaches the last cell that's already been queued for the section and moves to the next section. Only the first 2 sections are queued initially on this screen until the user scrolls vertically, so the accessibility focus only reaches the second section and then stops.
I see the same behavior using the Modern CollectionView demo app from Apple and turning the Accessibility Inspector on for the Orthogonal Section screens.
Does anyone know if this is the expected behavior and if there's a way to allow the sections to scroll horizontally to the end when using VoiceOver / Accessibility Inspector?