Not sure if this is something you folks would be willing to do but I figured it's worth asking about.
There is a known issue in VirtualBox that causes Win10 guests to flicker when 3D acceleration is enabled and the host uses Nvidia graphics. Apparently, Virtualbox has to leave it as-is because one of their paying customers needs it this way.. so everyone else has to deal with flickering problems. If it wasn't for that one customer, the patched version would be the default.
Blog post overview: https://techblog.devlat.eu/2017/04/07/screen-flickering-in-virtualbox-with-3d-enabled/
Full situation discussed here: https://www.virtualbox.org/ticket/13653
Official patch here: https://www.virtualbox.org/attachment/ticket/13653/vbox-NVIDIA-fix-v2.patch.txt
It would be nice if the maintainers here could apply this patch to the VBox package distributed in the repo.