libstdc++6-32bit from Geckito:SDK:Main project
Select Your Operating System
Add repository and install manually
For 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Geckito:SDK:Main/15.3/Geckito:SDK:Main.repo zypper refresh zypper install libstdc++6-32bit