I used to like the slide-out Panels, too.
Anyway, testing my apps in Big Sur, they generally run OK.
However, Ive noticed that sheet windows dont work as they used to.
Instead of a slide down from the top of the window, they appear in an unpredictable (to me) location on screen, and because they have no title bar, cannot be moved.
This makes sheet window style pointless in Big Sur
Is this a Xojo thing (I’m using 2018 to compile on Mac at the mo), a Big Sur thing, or yet another case of ‘Upgrade X, lose Y’ ?