For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ingogoeppert:work:gcc12/openSUSE_Tumbleweed/home:ingogoeppert:work:gcc12.repo
zypper refresh
zypper install cross-arm-none-gcc12-bootstrap
For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ingogoeppert:work:gcc12/openSUSE_Slowroll/home:ingogoeppert:work:gcc12.repo
zypper refresh
zypper install cross-arm-none-gcc12-bootstrap