Is the screenshot from the Guest or the Host?
I'm confused 'cause that's Ubuntu running with GNOME with the graphical glitch which would indicate it's the guest, but we're in the Windows Guests section, so... is it?
Well, assuming it's the Guest, I'd say that it's probably Wayland not being properly supported in the latest release.
There are a lot of commits made recently to support Wayland guests and you could try the latest development snapshot builds from here if you want to
https://www.virtualbox.org/wiki/Testbuilds and provide some feedback or you could just go back to the good old reliable xorg x11. At the beginning, before you click on your username to login, you're gonna see an engine in the bottom right corner. Click on it and choose GNOME on Xorg instead of "GNOME" (without anything), then login. This will make GNOME use X11 instead of Wayland and the glitch should disappear.
This is how it looks like on my Fedora
- GNOME on Xorg.png (17.28 KiB) Viewed 1625 times
so I suppose it should be something like this in Ubuntu:
- Screenshot from 2024-04-04 13-46-43.png (23.35 KiB) Viewed 1624 times