I thought that the problem of "iconv -l" not displaying the additions from glibc_gconv had been fixed, but, after checking the bug report, I found that the commit had not been applied until glibc-2.43.
After a long search for the commit, I applied it to glibc-2.42 and recompiled to get a new iconv/iconvconfig, but it doesn't appear to fix the problem.
glibc_gconv reposted with a startup script to create an actual file /usr/lib/gconv/gconv-modules.d/gconv-modules-extra.conf rather than a symlink.