For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ithod:updated/openSUSE_Tumbleweed/home:ithod:updated.repo
zypper refresh
zypper install gnucash
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ithod:updated/15.6/home:ithod:updated.repo
zypper refresh
zypper install gnucash
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ithod:updated/15.5/home:ithod:updated.repo
zypper refresh
zypper install gnucash