package-update-indicator from home:manfred-h:X11:xfce:4.21 project
Select Your Operating System
Add repository and install manually
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:manfred-h:X11:xfce:4.21/15.6/home:manfred-h:X11:xfce:4.21.repo zypper refresh zypper install package-update-indicator