Actual permissions of a project is union of permissions from all sources, including those inherited from parent projects, and those assigned to it directly.

Make sure not to make parent project visible if you do not want to open all subprojects. Instead, make each subproject visible separately as necessary.

From the usage point of view, if the parent project is not visible, then the child project is not visible, even if you set it visible.

From the usage point of view, if the parent project is not visible, then the child project is not visible, even if you set it visible

Make child visible while hide parent is totally valid, for instance if parent is only for setting inheritance purpose.

The only purpose is to make the project have a tree structure, when there are many projects, it looks more clear, if the parent project is not visible, it is not different from not using the parent project for me

how to set invisible, it seems that you can only control permissions by setting User Authorizations of the parent project.

Like mentioned before, you can make parent invisible, and set permission to make selected child projects visible to certain groups (or publicly).

If it does not work as expected, please tell me the detailed reproducing steps

I already known how to do it , I made a mistake ,thanks