Recent libstdc++ has a _dl_find_object@GLIBC_2.35 dependency, so it's not exactly trivial anymore to link a C++ program against a older, side-installed glibc version because it won't have that symbol. It's possible to work around that (link against a stub that has _dl_find_object@GLIBC_2.35 as a compat symbol, so that libstdc++ isn't rejected), but linking statically is much more difficult because libstc++.a (actually, libgcc_eh.a) does not have the old code anymore that _dl_find_object replaces (once GCC is built against a glibc version that has _dl_find_object).

This applies to other libraries as well because there are new(ish) math functions, strlcpy, posix_spawn extensions etc. that seem to be quite widely used already.