There are three errors in your system.
First, one of your repositories is not signed and requires a GPG key.
Secondly, your sources.list has duplicate sources.
Third, your system has a corrupted package.
Adding the proper signatures.
Run the following command in a terminal:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys F716E939977FC428
Update:
sudo apt update
Fixing the duplicate entries.
Install the Y-PPA-MANAGER:
sudo add-apt-repository ppa:webupd8team/y-ppa-manager
sudo apt upgrade
sudo apt install y-ppa-manager
Open the Y-PPA-MANAGER:
sudo y-ppa-manager
Navigate to Advanced → Scan and remove duplicate PPAs.
Let it complete and run:
sudo apt update
To fix the corrupted package:
First, update the repositories:
sudo apt update
Now, run:
sudo apt download runit-systemd && sudo dpkg -i --force-all ./*.deb
Run force install:
sudo apt -f install
This will also install the package you wanted to install i.e scaleft-server-tools.
If you want you can purge reinstall the package. By running:
sudo dpkg -P scaleft-server-tools --force-all && sudo apt install scaleft-server-tools
Alternatively, you can manually edit the post-installation files for the package scaleft-server-tools and replace the systemctl command with the service command and run sudo apt -f install.
Reboot to confirm all the changes.
That's it!
Good Luck!
EDIT
For problem #3 i.e Corrupted package.
In the documentation, I found that for Ubuntu 20.04 Focal or above, you need to explicitly allow certificate authorities (CAs) to use the ssh-rsa algorithm to sign certificates.
To do this, you need to add the following line to your OpenSSH daemon file (which is either /etc/ssh/sshd_config or a drop-in file under /etc/ssh/sshd_config.d/):
CASignatureAlgorithms +ssh-rsa
