How to create multiwindow?

[QiCodeCN]

There is a passage in the document：

A typical Flet program ends with a call to flet.app() where the app starts waiting for new user sessions. Function main() is an entry point in a Flet application. It's being called on a new thread for every user session with a Page instance passed into it. When running Flet app in the browser a new user session is started for every opened tab or page. When running as a desktop app there is only one session created.

Actually open a pc desktop application as follow：
ft.app(target=main)

Now, I want create new app(window) from main app. how to realize?
Can anyone give me some advice? Thank you very much.