If you get an error that you cannot create a file inside a folder when building in Whitebox Packages, take a look at where the original file is located.
If the file is located within your user folder, you might check and see if you’ve given permission to your
~/Downloads folder. Or perhaps you’ve given Full Disk Access even.
Somehow, even with these permission set I continue to get this error. I am currently running Big Sur 11.2 and Packages 1.2.9, current as of this writing. I have found that a good workaround is to stage the files I am using in my package in the
/Users/Shared folder. The permissions are more open in that folder as its intended for multiple users to access. If I shift the location of the files to be used into that folder I can successfully build.