For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:darix:apps/openSUSE_Tumbleweed/home:darix:apps.repo
zypper refresh
zypper install nextcloud-apps-bookmarks
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:darix:apps/16.0/home:darix:apps.repo
zypper refresh
zypper install nextcloud-apps-bookmarks
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:darix:apps/15.6/home:darix:apps.repo
zypper refresh
zypper install nextcloud-apps-bookmarks