There is a small yard on the first floor of the building. Is it illegal to cover all the courtyards? Do I need to apply? Can the property be managed? Good people, please help.

It is indeed illegal. I can't apply for this because there is no reason to apply.

In this case, the property has only the right of dissuasion, not the right of enforcement. If enforcement and punishment are needed, the local housing management department has the power.

If this kind of closure is not obvious, or many people in the community have already done so, and no one reports it, the competent authorities will not strictly enforce the law.