I have a headache and have no time to read your poorly annotated code carefully. I answer according to my experience:

Hope effect 1: I want to pop up a login box before entering the system main window.

Add the system's Main method to the login window instead of the system window.

After successfully logging in, call the system window again.

Effect 2: Make menu items unavailable.

It seems that many controls are inherited from composite controls. There are several methods for composite controls:

Settings can be edited

setEnable

setVisble

Generally speaking, to make a control unavailable, just use setEnable.

SetVisible(false) can also be ~ ~