I recently reformatted my computer and proceeded to install Virtualbox, which I use extensively for development and making videos. While my Windows 10 VM worked without issues, I noticed that my Linux VM would not resize correctly when using my host OS's window snapping feature (feature in Windows 10 and many Linux distros where the application 'snaps' to the right or left half of screen), and would retain the scrollbars. This annoyed the crap out of me, who immediately tried several things, including different Nvidia drivers and re-reformatting.
I was finally able to resolve the issue by going back a minor version, and using Virtualbox 6.0 instead of 6.1. Im not sure exactly what changed in 6.1, but this seemed to have resolved my problem and the snapping / auto resizing works perfectly again.
I know that this is different than most of my posts, but I was not able to find a solution in the traditional channels (Virtualbox forums and Stackoverflow), so figured I would post here in case it can help someone else.