As of glibc 2.34, the CSU has been hardened to remove the useful gadgets. This patch is the offendor, and it essentially removes __libc_csu_init (as well as a couple other functions) entirely.
Unfortunately, changing this breaks the ABI (application binary interface), meaning that any binaries compiled in this way can not run on pre-2.34 glibc versions - which can make things quite annoying for CTF challenges if you have an outdated glibc version. Older compilations, however, can work on the newer versions.