I do not like the default Debian 11 “Homeworld“ desktop theme at all.

Here is how to switch back to “futurePrototype” the default theme of Debian 10, but without displaying “Debian 10” anywhere:

sudo update-alternatives --config desktop-theme

Pick the /usr/share/desktop-base/futureprototype-theme.

Then to ensure we use the “nologo” background for the login manager:

sudo update-alternatives --install /usr/share/images/desktop-base/login-background.svg desktop-login-background /usr/share/desktop-base/active-theme/login/background-nologo.svg 100

Now you should see background-nologo.svg as the activated option for the desktop-login-background:

sudo update-alternatives --config desktop-login-background

The desktop-theme change also affects the background image of the grub boot loader, so we need to run this:

sudo update-grub

The next time we boot the system we should see background images from the configured theme for

• Grub boot screen
• Login manager (for example lightdm)
• Desktop (for example XFCE)