For anyone else stumbling on this post like I did... I verified OP @NicolasBrunnerSRF post appears to be an issue in ipadOS 17.x; but is resolved in ipadOS 18.x. The code recognizes the horizontal size has changed; but SwiftUI doesn't reflect the change in the UI element from sheet to fullScreenCover. I haven't found a work around :-\ @NicolasBrunnerSRF thanks for sharing your .modal ViewModifier.

I am hitting this exact wall right now. Before finding this thread I did all the same things you commented - with the same results too :-/ I’m about to ditch Menu for a non-native menu solution because I really like the UX with a sheet being presented from the menu. What did you end up doing?