Fixed in unstable/bullseye.
- Bug#932014: lib32stdc++-9-dev-x32-cross: Missin... Thomas Vincent
- Bug#932014: lib32stdc++-9-dev-x32-cross: M... Matthias Klose
- Bug#932014: marked as done (lib32stdc++-9-... Debian Bug Tracking System
Fixed in unstable/bullseye.