Extremely undiscoverable way to delete target and project level build settings. (i.e. reverting to iOS / MacOS defaults)
Hint: Deleting the text is not enough
P. S. Another subtle gotcha: Although you can edit project level build settings while viewing the target build settings, you cannot delete them. First select the project, then delete.
Best breakdown yet of using static libraries and build settings in Xcode. Although it seems that Xcode Workspaces are still very much broken…