The expression return $this->belongsTo(...t\Models\Import::class) returns the type Illuminate\Database\Eloquent\Relations\BelongsTo which is incompatible with the documented return type void.
The type Ladybirdweb\ImportExport\Models\Import was not found. Maybe you did not declare it correctly or list all dependencies?
The issue could also be caused by a filter entry in the build configuration.
If the path has been excluded in your configuration, e.g. excluded_paths:["lib/*"],
you can move it to the dependency path list as follows: