You actually need to be a member in order to see the investigations sub.
reference.
I'm able to view it despite being a newbie, is it due to the whole Copper Member privilege?
Probably yes. Copper membership gives you some of the member rank privileges, but I'm not sure if theymos intentionally allowing Copper member to access investigation board though.
- Some of the same permissions as Member-rank members, such as reduced signature styling restrictions. (But none of the PM-related restrictions are currently lifted, such as the style limit or per-hour PM limit.)