For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Geckito:SDK:Main/openSUSE_Factory/Geckito:SDK:Main.repo
zypper refresh
zypper install cross-avr-gcc9
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Geckito:SDK:Main/15.6/Geckito:SDK:Main.repo
zypper refresh
zypper install cross-avr-gcc9
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Geckito:SDK:Main/15.5/Geckito:SDK:Main.repo
zypper refresh
zypper install cross-avr-gcc9