xcconfig has no effect when running 'swift package generate-xcodeproj'

I am creating an xcode proj with swift package generate-xcodeproj. The resulting project has a few targets, that correspond to the dependencies of the project. Some of them have IPHONEOS_DEPLOYMENT_TARGET set to 8.0, some to 13.5, and the compilation fails, saying:

Compiling for iOS 8.0, but module 'SwiftProtobuf' has a minimum deployment target of iOS 13.5

If I go manually into the build settings of the generated xcodeproj and change IPHONES_DEPLOYMENT_TARGET of all the targets to 13.5, then it builds.

So I tried to create a build.xcconfig and generating the xcodeproj with the following content and command:

build.xcconfig:

IPHONEOS_DEPLOYMENT_TARGET[sdk=iphoneos*] = 13.5
swift package generate-xcodeproj --xcconfig-overrides build.xcconfig

But this has no effect. If I git add the xcodeproj after I run swift package generate-xcodeproj, and then run swift package generate-xcodeproj --xcconfig-overrides build.xcconfig, I don't see any diff. Which suggests that it has absolutely no impact, right?

How should I use xcconfig to set the IPHONEOS_DEPLOYMENT_TARGET of all the targets of the generated xcodeproj?