For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:libraries:c_c++/openSUSE_Factory/devel:libraries:c_c++.repo
zypper refresh
zypper install criterion
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:libraries:c_c++/15.6/devel:libraries:c_c++.repo
zypper refresh
zypper install criterion
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:libraries:c_c++/15.5/devel:libraries:c_c++.repo
zypper refresh
zypper install criterion