We’ll see when they ship, but based on what I’ve heard so far, I assume macOS will insert whitespace as necessary to move any overlapping menus to the right of the notch.
If there are so many menus that they can’t all fit, the system will try to squeeze them closer together, then will hide lower-priority widget menus (e.g. the Bluetooth or audio volume menus). And if necessary, it will truncate the menu titles to make them fit. See also Menu Bar Menus - Menus - macOS - Human Interface Guidelines - Apple Developer. (h/t @ddmiller for the links).
But given the size and resolution of these displays, I think it would be a pretty poorly designed app that put up so many menus that this became an actual problem.
My main Mac has an old 1200p (1920x1200) display and I can’t think of any app that puts up so many menus that they reach to the center of the screen. The widest I’ve got is Photoshop Elements, and that’s primarily because they violated Apple’s rule and made the app menu (which is supposed to be a short form of the app’s name) “Adobe Photoshop Elements 2021 Editor”. (Apparently, “Photoshop Elements” wasn’t good enough for them. )
The developer guide for the notch focuses primarily on full-screen mode, where there might not be a menu bar. For compatibility with old apps, the entire height of the notch-area will be beyond the edge of the app (presumably with the menu bar filling in the space when it appears).
Developers can also choose to use the entire screen. If they do, then they are responsible for not drawing anything meaningful behind the notch. There are APIs so they will know where these screen regions are. See also Full-Screen Mode - App Architecture - macOS - Human Interface Guidelines - Apple Developer