Need High Res Ubuntu in VirtualBox

I guess you are limited by the video card that Windows VirtualBox provides to the Ubuntu VM. Normally you can choose different models, increase video RAM, that kind of thing.

(Or just use some "paravirtualized" display that doesn't simulate real hardware- basically the Ubuntu VM knows how big the VirtualBox window is, and adjusts its resolution automatically.)

I'm not sure what's the current situation on Windows- I'm not sure HyperV is available on all editions, or whether people are still using VirtualBox. People I interact with stopped using VirtualBox long time ago. It might be worthwhile to use WSL instead. It's a well-integrated VM provided by Windows to run Linux apps- it can do graphical apps very nicely. Stuff might just work OOB (start Ubuntu in WSL, run app, done).

If you set the Virtualbox VM video adapter to "VMware SVGA", you should be able to define nearly any arbitrary resolution. Also, if you have the Virtualbox Integration components installed in the VM, by default, the VM will automatically set the display resolution to whatever the host window viewport size is.