There is an "Encrypt contents to secure data" checkbox for every folder on the drive, except the root folder. It's accessible by right-clicking a folder, and selecting "Advanced" properties:
One of its effects is to make any new file in this folder be EFS-encrypted.
I want any new file in the root of my drive D:\ to also be encrypted. However, this checkbox is missing from the drive properties dialog. Is there any way to apply this attribute to the root folder, so that new files in the root get encrypted?
Before you bring up full-disk encryption, remember that the two have completely different use-cases, in particular full-disk encryption is more limited in terms of what's possible with regard to multi-user environments.