For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:frispete:musescore/openSUSE_Tumbleweed/home:frispete:musescore.repo
zypper refresh
zypper install musescore
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:frispete:musescore/15.5/home:frispete:musescore.repo
zypper refresh
zypper install musescore
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:frispete:musescore/15.4/home:frispete:musescore.repo
zypper refresh
zypper install musescore