Are employees of public institutions allowed to work part-time outside the home?

Public institution staff are definitely not allowed to work part-time outside, but this is not allowed because the company knows that you have another job outside, so it will not allow it. But if you are a creator, for example, you can create online during your spare time, whether it is literary or other creations, these are your legal income. This kind of work is allowed as long as it does not affect the normal workplace. However, what is expressly prohibited by the employer is that you have another job outside, get another salary, and even go to work in the same place as the other job. This situation is definitely prohibited. Because public institutions also belong to a large category of civil servants within the scope of the national establishment.