So I’ve read that materials in sketchup are located in the hidden library folder on macs , which I located : Library > Application Support > Sketchup 2023 > Sketchup > Material. However this folder is empty. I read an old thread from 2018 with the same issue saying the materials one adds from in Sketchup itself are located in the Program Data Folder but I can’t find this on a mac.
Can Anyone help please?
the place where you’re looking at right now contains the user materials.
the ones you eventually created.
if you want the default sketchup stuff, you’ll have to dig elsewhere :
in you application folder, find sketchup pro. right click on it and show content.
there, it’s content / ressources / content / materials
here you’ll find the basic materials SU is shipped with.
you’ll find other default things like default styles.
To find where user-defined materials and collections are, open SketchUp ->Settings → Files and look at the entry for Materials. You can even open that folder by clicking the icon at the right.
@ateliernab correctly pointed out that app-defined materials are not kept there, they are kept inside the app itself. But from your post title, I think you are not looking for SketchUp’s standard materials, you are looking for the ones you have added. If you really want to see where the built-in materials are, just beware that you mess around inside the app bundle at your own risk.
BTW Program Data is a Windows thing, not on Mac.
I assumed they were looking for the default one because the path they give
is the standard location you’ll see in settings/files
Unless off course they’ve changed the location in the settings 
if you didn’t change the path, and you’re looking for the materials you made, well right now it means you have non. how did you save them ?
Also beware that there is an all-users Library (“/Library”) and your personal Library (“/Users/yourname/Library”, abbreviated as “~/Library”). They are not the same. Your materials are normally stored in the latter unless you specify somewhere else, which is allowed so that you can share materials across SketchUp versions.
And, normally, the Library folder is not visible by default.
You must press the Option key and keep it pressed and then choose the Go menu in the Finder to see Library in the pull down menu.
Thank you! I have been searching for that folder for hours! You saved me