For Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:plater:lilypond/Tumbleweed/home:plater:lilypond.repo
zypper refresh
zypper install liblo
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:plater:lilypond/15.6/home:plater:lilypond.repo
zypper refresh
zypper install liblo
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:plater:lilypond/15.5/home:plater:lilypond.repo
zypper refresh
zypper install liblo