Maintainers for g++-9 are Debian GCC Maintainers <[email protected]>.
You may want to refer to the following packages that are part of the same source: cpp-9, g++-9-multilib, gcc-9, gcc-9-base, gcc-9-hppa64-linux-gnu, gcc-9-locales, gcc-9-multilib, gcc-9-offload-nvptx, gcc-9-plugin-dev, gcc-9-source, gcc-9-test-results, gccbrig-9, gccgo-9, gccgo-9-multilib, gdc-9, gdc-9-multilib, gfortran-9, gfortran-9-multilib, gm2-9, gnat-9, gobjc++-9, gobjc++-9-multilib, gobjc-9, gobjc-9-multilib, lib32asan5, lib32gcc-9-dev, lib32gfortran-9-dev, lib32go-9-dev, lib32go14, lib32gphobos-9-dev, lib32gphobos76, lib32objc-9-dev, lib32stdc++-9-dev, lib32stdc++6-9-dbg, lib64asan5, lib64gcc-9-dev, lib64gfortran-9-dev, lib64go-9-dev, lib64go14, lib64gphobos-9-dev, lib64gphobos76, lib64objc-9-dev, lib64stdc++-9-dev, lib64stdc++6-9-dbg, libasan5, libgcc-9-dev, libgccjit-9-dev, libgccjit-9-doc, libgfortran-9-dev, libgm2-0, libgm2-9-dev, libgnat-9, libgnatvsn9, libgnatvsn9-dev, libgo-9-dev, libgo14, libgphobos-9-dev, libgphobos76, libhsail-rt-9-dev, libobjc-9-dev, libstdc++-9-dev, libstdc++-9-doc, libstdc++-9-pic, libstdc++6-9-dbg, libx32asan5, libx32gcc-9-dev, libx32gfortran-9-dev, libx32go-9-dev, libx32go14, libx32gphobos-9-dev, libx32gphobos76, libx32objc-9-dev, libx32stdc++-9-dev, libx32stdc++6-9-dbg.
You might like to refer to the g++-9 package page, to the Package Tracking System, or to the source package src:gcc-9's bug page.
If you find a bug not listed here, please report it.