I want to install multiple desktops in 1 partition.
Do Sparky offers a desktop environment, including its own theme as (deb) package?
or This should be I install the package that provides Debian is?
To install the Debian package,
if there is a means for applying such as Sparky theme, please tell me it.
No, tere is not something like sparky desktop/meta packages (yet).
Simply install any desktop provided by Debian devs, then install sparky theme, wallpaper, icons, etc. and set it as you like.
I want to maintain the desktop environment that was installed from some of the ISO.