It seems as though the way the MarketingCloudSDK Swift Package Module is built that it cannot be included in projects that use a different version of the Swift compiler. When trying to use the Swift Package for 8.0.3 in my team's project we get the following error:
Failed to build module 'MarketingCloudSDK'; this SDK is not supported by the compiler (the SDK is built with 'Apple Swift version 5.4 (swiftlang-118.104.22.168 clang-122.214.171.124)', while this compiler is 'Apple Swift version 5.5.2 (swiftlang-1300.0.47.5 clang-1300.0.29.30)'). Please select a toolchain which matches the SDK.
We are building with the latest Xcode, version 13.2.1.
There is an issue on Stack Overflow similar to this with possible resolution steps: https://stackoverflow.com/questions/70556401/swift-version-conflict-this-sdk-is-not-supported-by-the-compiler-please-select
import MarketingCloudSDKand I get the same issue. So I don't believe it is any particular setting in our project.