I believe there are graphics problems in the Ubuntu 24.04 releases.
I’m running Kubuntu 24.04, with an nVidia GeForce GTX 1060 6GB video card. I use Xwindows, not Wayland. All the software is up to date, including the proprietary nVidia driver. After running for a while, newly created windows will open as black boxes. Dragging the windows around doesn’t help. Resizing the windows sometimes causes the content of the window to be visible, but often not. Closing some open applications often temporarily resolves the problem, especially closing Firefox with many open tabs.