Re: C23 auto x C++ auto.

"typeof" and "auto" have been available forever as gcc extensions (where "auto" was spelt "__auto_type", since of course "auto" had another meaning in C until C23).  One use-case for C is in macros that handle multiple types, but I expect people have done other things with them too.
 It would have been nice to see statement expressions included in C23, as they have been in gcc for ages:
 #define max(a,b) \
   ({ __auto_type _a = (a); \
       __auto_type _b = (b); \
     _a > _b ? _a : _b; })
  In general, it's just another tool that could be useful in writing code that's a bit more flexible.