Comment 28 for bug 1892367

So this is fixed now (thx to Brian).
 s390-tools | 2.12.0-0ubuntu3.3 | focal-proposed | s390x
 s390-tools-signed | 2.12.0-0ubuntu3.3 | focal-proposed | s390x
respectively
 s390-tools | 2.14.0-1ubuntu1.2 | groovy-proposed | s390x
 s390-tools-signed | 2.14.0-1ubuntu1.2 | groovy-proposed | s390x

After activating proposed:
sudo add-apt-repository "deb http://us.ports.ubuntu.com/ubuntu-ports/ $(lsb_release -sc)-proposed main"
sudo apt update
s390-tools installs fine (and pulls in s390-tools-signed):
sudo apt install s390-tools
as one can check with:
dpkg -l | grep s390-tools
Wold yu please give it another try for verification?