How can I Remove/Hide Default Materials Collections on Sketchup 2021 on Windows?

I have also tried looking for the folder under program files but it isn’t available under there anymore.

Try here:
c:\Users\All Users\SketchUp\SketchUp 2021\SketchUp\

Or inside here ?
C:\ProgramData\SketchUp\SketchUp 2021

Dig deeper in the ProgramData/SketchUp/SketchUp 2021/SketchUp