I presume you have downloaded the 21GB full installer, unpacked all of it into a folder, then run the “Setup” program. If not, that is what you need to do. If you have, I would run the installer over again.
If that doesn’t fix it, open Steinberg Library Manager and see if you see the content. If not, find the missing content in the “Additional Content\VST Sound” of your unpacked installer, and double click a file in each folder (you only need do one per folder - Library Manager should install all the other files in that folder at the same time).