Actually lots is still on C89.

I'm trying to drag one program at $employer up to C99 (plus C11 _Generic), so I can then subsequently drag it to the bits of C23 which GCC 13 supports.

This all takes times, and having to convince colleagues during code reviews.

What C23 has done is authorise some of the extensions which GCC has had for some time as legitimate things (typeof, etc).

However the ability to adopt is also limited by what third party linters in use at $employer may also support.