For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mimosius:Archiving:Backup/openSUSE_Tumbleweed/home:mimosius:Archiving:Backup.repo
zypper refresh
zypper install backintime
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mimosius:Archiving:Backup/15.6/home:mimosius:Archiving:Backup.repo
zypper refresh
zypper install backintime
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mimosius:Archiving:Backup/15.5/home:mimosius:Archiving:Backup.repo
zypper refresh
zypper install backintime