If the company terminates the employment contract on the grounds of "incompetence", how can one determine whether this is illegal? What evidence should be preserved?

If an employer terminates a labor contract on the grounds of "incompetence in the job", it must prove that the worker is incompetent, that he/she has received training or been reassigned to another position but still remains incompetent, and that the employer has followed the legal procedures. The worker should keep materials such as the labor contract, assessment records, termination notices, and communication records.