SwiftUI problem in existing project

I want to start and integrate SwiftUI in an existing project. For starters I've added a SwiftUI file. There's a problem with the preview of this file, it is paused. When I hit the resume button, I see that an error occurs:

remark: Incremental compilation has been disabled: it is not compatible with whole module optimization

Command CompileSwiftSources failed with a nonzero exit code

Above it, there are no hints to what this nonzero exit code could be, or what is causing it.

Does anyone have a pointer for me on how to resolve this? Needless to say that the preview works fine in a new project.

SwiftUI problem in existing project
 
 
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