Hi @eheimbuch,
thank you for your reply. As I learned, there is no system keyring service on many headless linux distros (Ubuntu server or even WSL). I was able to install the GNOME Keyring daemon.
sudo apt install gnome-keyring
dbus-run-session -- sh
echo -n "your_master_password" | gnome-keyring-daemon --unlock
Now you can use scm CLI in this special shell.