Para 15.6 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:zippy:jx:packages-ready/15.6/home:zippy:jx:packages-ready.repo
zypper refresh
zypper install frox
Para 15.5 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:zippy:jx:packages-ready/15.5/home:zippy:jx:packages-ready.repo
zypper refresh
zypper install frox
Para 15.4 execute o seguinte como root:
zypper addrepo https://download.opensuse.org/repositories/home:zippy:jx:packages-ready/15.4/home:zippy:jx:packages-ready.repo
zypper refresh
zypper install frox