The monitor resolution in our situation is 1920x1080, while the maximum resolution under Windows 10 guest settings is 1600x1200 (available resolution settings of the guest OS are not for widescreen displays, as you can see).
You can raise the guest OS resolution by going to Windows 10 display settings (right-click the desktop and select Display settings from the context menu), but you still can't use full screen mode. Acceleration in 2D and 3D can also be enabled.
Setting 128 MB of video memory is suggested because when using a video mode with a higher resolution, more video memory is required. In the virtual machine settings, look at the amount of video RAM you have. The size of the guest OS user interface does not expand when you try to enlarge the VirtualBox VM window shortly after installing Windows 10 on a VirtualBox VM. As you may recall, VirtualBox is installed on the host OS, which runs on a real machine, and the guest OS, which runs on a virtual machine. In the Host Only mode, you may disconnect the internet connection or create a virtual network adapter for a VM to enable network communication only between the host and guest systems and prevent the Windows 10 guest from connecting to other networks, including the internet. Running Windows 10 as a virtual machine (VM) on VirtualBox is a smart choice if security is a concern. How to make VirtualBox VM full screen in Windows 11/10 Learn how to make VirtualBox full screen for Mac OS X and Windows guest OSs in today's blog article. But don't panic you may boost the screen resolution of the guest OS user interface and run it in full screen mode. Working in a guest OS with a low resolution is in most circumstances inconvenient. Furthermore, the size of the window is generally not large, and if the window's size is increased, the resolution of the guest OS user interface remains same.