When you installed wireplumber, pipewire-media-session was removed as both packages conflict with each other ... However, either package is essential for the desktop functionality ... Therefore, by installing pipewire-media-session, APT should take care of removing wireplumber safely like so:
$ sudo apt-get install pipewire-media-session
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The following packages will be REMOVED:
wireplumber
The following NEW packages will be installed:
pipewire-media-session
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Do you want to continue? [Y/n] y
ubuntu-desktop is a meta-package(a "container" of multiple packages) ... Some of those packages are essential and cannot be removed and the DE cannot function normally without them ... Therefore, if you remove any of those packages ubuntu-desktop will also be removed ... Some of them can be substituted with similar packages(like the two "above mentioned" session managers for pipewire), but even this can cause problems ... Better leave them alone(i.e. no removal/substitution).
Installing pipewire-media-session should only remove wireplumber ... ubuntu-desktop should not be removed at all ... However, I don't know what other package modifications you did on your system ... So be careful and read what APT prints as packages to be removed before you answer "yes" to it.
If, however, APT is still trying to remove ubuntu-desktop, then it means that other essential packages are missing … So, answer "no" to that and reinstall ubuntu-desktop like so:
sudo apt-get install --reinstall ubuntu-desktop
then, try again.
