Does GitHub support VFS for Git?
GitHub doesn't support VFS. There are news articles in 2017 saying GVFS and later VFS would be supported by GitHub. As of today, there is no support and no planned support for it.
My sources:

https://github.com/microsoft/VFSForGit/issues/1640
https://github.community/t/vfsforgit-setup/128184
https://github.community/t/microsofts-virtual-filesystem-for-git/2092
The Github public roadmap says nothing related to VFS or anything similar. https://github.com/github/roadmap