I'm having a similar issue. I'm a co-author, and I'm unable to create any statblocks in the shared campaign we're running.

Yeah I didn't know how to word this or even if I put this into the correct category

This is not a bug - depending on the feature, co-authors may not have access to it

Creating Sheets or any other studio tool which is under an account and not world are certainly included to those features co-authors of a world do not have access to