As per this topic, I found that, after accepting the prompt to purge unused objects, the default materials were also deleted.
Unfortunately, it doesn’t look like all of the default materials are available in the materials library - at least, the glass materials available in the library are much more opaque than the one found in the default materials.
Would you consider adding a “Default Materials” folder to the materials library, please? So that these aren’t lost forever after accepting the prompt to purge unused objects.
I tested what you described, and all of the standard materials are still there after doing a purge. In materials, are you still on the house icon, or did you try clicking the magnifier icon?
I see the same as Colin. Purging unused components does not purge In Model materials.
If you want to keep those added materials for later use, you can save the model file with the components and materials and import it into your project when you need it. After applying the desired materials to your project, delete the unneeded component and purge unused from Components and Materials
