Maintainers for g++-multilib are Debian GCC Maintainers <debian-gcc@lists.debian.org>.
You may want to refer to the following packages that are part of the same source: cpp, cpp-aarch64-linux-gnu, cpp-arm-linux-gnueabi, cpp-arm-linux-gnueabihf, cpp-for-build, cpp-for-host, cpp-i686-linux-gnu, cpp-mips64el-linux-gnuabi64, cpp-powerpc64le-linux-gnu, cpp-riscv64-linux-gnu, cpp-s390x-linux-gnu, cpp-x86-64-linux-gnu, g++, g++-aarch64-linux-gnu, g++-arm-linux-gnueabi, g++-arm-linux-gnueabihf, g++-for-build, g++-for-host, g++-i686-linux-gnu, g++-mips64el-linux-gnuabi64, g++-multilib-i686-linux-gnu, g++-multilib-s390x-linux-gnu, g++-multilib-x86-64-linux-gnu, g++-powerpc64le-linux-gnu, g++-riscv64-linux-gnu, g++-s390x-linux-gnu, g++-x86-64-linux-gnu, gcc, gcc-aarch64-linux-gnu, gcc-arm-linux-gnueabi, gcc-arm-linux-gnueabihf, gcc-for-build, gcc-for-host, gcc-hppa64-linux-gnu, gcc-i686-linux-gnu, gcc-mips64el-linux-gnuabi64, gcc-multilib, gcc-multilib-i686-linux-gnu, gcc-multilib-s390x-linux-gnu, gcc-multilib-x86-64-linux-gnu, gcc-offload-amdgcn, gcc-offload-nvptx, gcc-powerpc64le-linux-gnu, gcc-riscv64-linux-gnu, gcc-s390x-linux-gnu, gcc-x86-64-linux-gnu, gccbrig, gccgo, gccgo-aarch64-linux-gnu, gccgo-arm-linux-gnueabi, gccgo-arm-linux-gnueabihf, gccgo-for-build, gccgo-for-host, gccgo-i686-linux-gnu, gccgo-mips64el-linux-gnuabi64, gccgo-multilib, gccgo-multilib-i686-linux-gnu, gccgo-multilib-s390x-linux-gnu, gccgo-multilib-x86-64-linux-gnu, gccgo-powerpc64le-linux-gnu, gccgo-riscv64-linux-gnu, gccgo-s390x-linux-gnu, gccgo-x86-64-linux-gnu, gdc, gdc-aarch64-linux-gnu, gdc-arm-linux-gnueabi, gdc-arm-linux-gnueabihf, gdc-for-build, gdc-for-host, gdc-i686-linux-gnu, gdc-mips64el-linux-gnuabi64, gdc-multilib, gdc-multilib-i686-linux-gnu, gdc-multilib-s390x-linux-gnu, gdc-multilib-x86-64-linux-gnu, gdc-powerpc64le-linux-gnu, gdc-riscv64-linux-gnu, gdc-s390x-linux-gnu, gdc-x86-64-linux-gnu, gfortran, gfortran-aarch64-linux-gnu, gfortran-arm-linux-gnueabi, gfortran-arm-linux-gnueabihf, gfortran-for-build, gfortran-for-host, gfortran-i686-linux-gnu, gfortran-mips64el-linux-gnuabi64, gfortran-multilib, gfortran-multilib-i686-linux-gnu, gfortran-multilib-s390x-linux-gnu, gfortran-multilib-x86-64-linux-gnu, gfortran-powerpc64le-linux-gnu, gfortran-riscv64-linux-gnu, gfortran-s390x-linux-gnu, gfortran-x86-64-linux-gnu, gm2, gm2-aarch64-linux-gnu, gm2-arm-linux-gnueabi, gm2-arm-linux-gnueabihf, gm2-doc, gm2-for-build, gm2-for-host, gm2-i686-linux-gnu, gm2-mips64el-linux-gnuabi64, gm2-powerpc64le-linux-gnu, gm2-riscv64-linux-gnu, gm2-s390x-linux-gnu, gm2-x86-64-linux-gnu, gobjc, gobjc++, gobjc++-aarch64-linux-gnu, gobjc++-arm-linux-gnueabi, gobjc++-arm-linux-gnueabihf, gobjc++-for-build, gobjc++-for-host, gobjc++-i686-linux-gnu, gobjc++-mips64el-linux-gnuabi64, gobjc++-multilib, gobjc++-multilib-i686-linux-gnu, gobjc++-multilib-s390x-linux-gnu, gobjc++-multilib-x86-64-linux-gnu, gobjc++-powerpc64le-linux-gnu, gobjc++-riscv64-linux-gnu, gobjc++-s390x-linux-gnu, gobjc++-x86-64-linux-gnu, gobjc-aarch64-linux-gnu, gobjc-arm-linux-gnueabi, gobjc-arm-linux-gnueabihf, gobjc-for-build, gobjc-for-host, gobjc-i686-linux-gnu, gobjc-mips64el-linux-gnuabi64, gobjc-multilib, gobjc-multilib-i686-linux-gnu, gobjc-multilib-s390x-linux-gnu, gobjc-multilib-x86-64-linux-gnu, gobjc-powerpc64le-linux-gnu, gobjc-riscv64-linux-gnu, gobjc-s390x-linux-gnu, gobjc-x86-64-linux-gnu, libgphobos-dev.
You might like to refer to the g++-multilib package page, to the Package Tracking System, or to the source package src:gcc-defaults's bug page.
If you find a bug not listed here, please report it.