The issue is that the Arch Linux debuginfod servers only store data for the latest version of a package. So when the Manjaro and Arch Linux glibc packages are out of sync, you can no longer download the debug information for glibc available in the Manjaro repositories, and valgrind needs that to work.
That is because 2.36-3 is the version that is available in the Arch Linux repositories, and the debug data for that can be downloaded from the Arch Linux debuginfod server.