After installing Windows Server 2008, there is no way to deploy to full screen, guest extension installed.


After frequent restarts, the problem resolved itself. I don’t even understand why from the very beginning it did not expand to full screen.

I think it's a known issue. I encountered a similar issue running Solus in a VM on a Debian Stable host. Use your favored search engine and search using the phrase virtualbox 1920x1080.