The reason for this is that the Ubuntu installer does not install the so called VirtualBox guest additions.

For example after resizing the virtual machine window or going into full-screen mode. If you ever installed Ubuntu in a VirtualBox virtual machine, you probably noticed that you can’t change the screen resolution. A newer version of this article is availabe, which covers the topic of how to install the VirtualBox Guest Additions in Ubuntu 22.04 “Jammy Jellyfish”. On the 21st of April 2022, the Ubuntu team released the successor Ubuntu 22.04 “Jammy Jellyfish”. This article explains how to install the VirtualBox guest additions in an Ubuntu virtual machine.

Besides automatically adjusting the screen resolution, you also get support for a bi-directional clipboard and shared folders.

Bummed that you can’t change the screen resolution in your freshly installed Ubuntu virtual machine? An easy fix exists for this: You just need to install the VirtualBox guest additions in your Ubuntu virtual machine.

Uninstall virtualbox ubuntu