Many users have C:\ with a small SSD and D:\ with a larger HDD.
Windows puts the user folders on C:\, which means that AppData, Downloads, and Documents for several users rapidly fill up the smaller disk. The whole point of the larger disk is user data.
Plenty of discussions (1, 2 3, 4, 5, 6, 7) make it clear that moving user data is difficult or risky, with sysprep, hardlinks, registry edits, and other deep technical work that is not suitable for non-technical users.
Even just moving Documents is blocked because of a link -- I think OneDrive did this -- putting Documents under C:\Users\MyName\OneDrive\Document. (And the user name is hardcoded instead of passed with a variable). And in any case, Documents is not the main culprit -- AppData is.
Is there an easy and safe way to set the user folders in D:\?
If not, it seems that the larger "data disk" with 900 GB is of little value other than perhaps manually moving movies to it.