Gentlemen, tell me.
You need a redirect to your html page after the user logs in to OpenWrt / Lede.
I dont understand.
Please be more specific.
After clicking the Login button, open my page.
No, we do not need to redirect to your page from our router configuration... or perhaps you intended to ask for something different...
In your screenshot, you are logging in to your router setup, not the OpenWrt/LEDE website.
In the www folder I put a new page index2.html, it should be opened by clicking the Login button. Which file is edited in Luci to open my index2.html?
As far as I remember either /usr/lib/lua/luci/controller/index.lua or /usr/lib/lua/luci/controller/status.lua or both. Check out the content of these files and ideally read up on the Luci Dispatcher.
PS. Alternatively, you can create your own controller and delete everything else.