For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Dead_Mozay:matrix/openSUSE_Tumbleweed/home:Dead_Mozay:matrix.repo
zypper refresh
zypper install cmark
For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Dead_Mozay:matrix/openSUSE_Slowroll/home:Dead_Mozay:matrix.repo
zypper refresh
zypper install cmark
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Dead_Mozay:matrix/15.5/home:Dead_Mozay:matrix.repo
zypper refresh
zypper install cmark