A: Those libraries are deprecated. If you need them, you can find archived links on the Chaos Forums, but they are not supported on modern render engines.
If you are upgrading from V-Ray Next or V-Ray 5, note that the old link structure is deprecated.
Do not try to manually link a V-Ray 5 library to V-Ray 6. You must download the V-Ray 6 specific library even if the material names look similar. The internal shader logic changed. vray 6 material library link
If you have 10 artists, do not download the library 10 times.
There is no single www.vray.com/materials page that hosts the raw files for download. Instead, the library is accessed inside your 3D software. However, you need the asset link to download the 50GB+ database. A: Those libraries are deprecated
If you move the library to an external SSD (highly recommended for speed) or reinstall your OS, you need to update the link manually.
If you want to browse before opening your 3D software: If you are upgrading from V-Ray Next or
C:\Program Files\Common Files\ChaosGroup\V-Ray_MaterialLibrary\