Quick answer: Unity Burst job referencing a managed delegate failing Burst validation? Delegate calls are managed; Burst rejects - use FunctionPointer or remove the call.
Job declares Action<int> field; Burst: cannot compile because of managed type.
Use FunctionPointer
public FunctionPointer<Action<int>> cb;Burst-compatible callable. Resolved at job creation.
Or move callback outside
Job populates data; main thread invokes callbacks after job completes.
Audit job fields
Each field must be Burst-compatible. Delegates, classes, strings: all managed.
“Managed types break Burst. Job design must respect the boundary.”
If you find yourself fighting Burst, the job design is suspect. Re-architecture for purity; performance follows.