Matcaps What are the file extentions for these files that I need to load?

How do I find out more about these install files ? Are they requred for Eevee to work. ?

Well, you don’t need to load them. They don’t really have anything to do with Eevee. Some people like to preview their models with a matcap while modeling, it’s particularly useful for sculpting.

You already have all the default ones available, if you want custom ones you can find some online or make your own. I think they’re just image files, nothing complicated.