xonotic-server from openSUSE:Backports:SLE-15-SP5:Update project
Select Your Operating System
Add repository and install manually
For standard run the following as root:
zypper addrepo https://download.opensuse.org/repositories/openSUSE:Backports:SLE-15-SP5:Update/standard/openSUSE:Backports:SLE-15-SP5:Update.repo zypper refresh zypper install xonotic-server