I compiled my plugin for R23 on a PC and no problems.
Now I want to do the same on the Mac (10.15.6) using Xcode 11.3.1.
I copied the sdk and the ran R23 projecttool to /Documents.
Everything seems ok, plugins.xcode was created and looks good.
Again, I am doing everything in my Documents folder, so I should not have any protection / privilege issues.
But I get the following IOError.