The Lua code to remove ELF multilibs does not iterate over all glibc-hwcaps subdirectories, so it misses the power9 multilib added in bug 1956357.
I misremembered how this works. During the update if the old and new glibc ship a multilib, it is replaced in place, so there is no issue. We cannot remove glibc-hwcaps multilibs proactively because doing so in %post would remove the already-overwritten new files. At the end of the RPM transaction, the glibc-hwcaps multilib would be gone, which is not what we want.