Same here. It seems to occur if I use import Playgrounds and the #Playground macro in a SPM module.
So far I haven't found a workaround. Just don't use the playground macro.
(Side note: Why do I feel that it happens all the time that features are made for WWDC presentations, but do not work at all in reality, and fail in the most basic setups? I came to the platform, because it didn't use to be that way…)
Topic:
Developer Tools & Services
SubTopic:
Xcode