If I want to modify the login background image (not themes app)?

Hey, everyone, if I want to use themes, how do I modify the login background image (not themes app)??

Easiest way is to enable theming app and change image.

Are you not able to enable this app?

Yes, I can open apps. But for some reason, I have to use the theme function.

When you installed the Themes-App, you can go to Settings > Theming and upload a new background image.

Yes, I can. But I don’t like to show Nextcloud and keep your date in maintenance mode.
So I want to be able to use the theme, but the documentation is not fully written, what should I do?:sob::sob::sob::sob: