For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:fusionfuture:joplin/openSUSE_Tumbleweed/home:fusionfuture:joplin.repo
zypper refresh
zypper install joplin-desktop
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:fusionfuture:joplin/16.0/home:fusionfuture:joplin.repo
zypper refresh
zypper install joplin-desktop
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:fusionfuture:joplin/15.6/home:fusionfuture:joplin.repo
zypper refresh
zypper install joplin-desktop
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:fusionfuture:joplin/15.5/home:fusionfuture:joplin.repo
zypper refresh
zypper install joplin-desktop