There are some errors with avahi-daemon when I try to upgrade Xubuntu 21.04
Solution 1:
You need to remove obsolete sysv-rc package and reinstall the corresponding package with invoke-rc.d inside it by
sudo dpkg -P --force-all sysv-rc
sudo apt-get install --reinstall init-system-helpers
and then retry running
sudo apt-get update
sudo apt-get install -f
sudo dpkg --configure -a