For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ecsos:Publishing/openSUSE_Tumbleweed/home:ecsos:Publishing.repo
zypper refresh
zypper install gscan2pdf
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ecsos:Publishing/15.6/home:ecsos:Publishing.repo
zypper refresh
zypper install gscan2pdf
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ecsos:Publishing/15.5/home:ecsos:Publishing.repo
zypper refresh
zypper install gscan2pdf