Xcode seems to always choose to link statically - any automatic heuristics are broken and have never worked, see this: How to link dynamically
There is also no way for a user to manually change the import to dynamic from static.
I would in fact advise that you add a dynamic library to your module so the consumer can choose to link once, especially if the target app uses multiple app extensions where each extension in-turn depends on the same library. This will increase the overall size of the app, and in case a shared framework is using the library, you'll see dozens of runtime errors about "duplicate symbols found" given both the framework plus the app is now statically linked to the swift package.
All popular swift packages at the moment offer both a static and a dynamic variant. For instance: