bug#50030: C-M-SPC is not working

[Eli Zaretskii]

> From: Pedro Delfino <p.delfino01@gmail.com>
> Date: Thu, 12 Aug 2021 14:25:10 -0300
> 
> 1 - Create an emacs lisp file, could be .emacs;
> 
> 2 - Insert any valid s-expression, could be 
> (load (expand-file-name "~/.quicklisp/slime-helper.el"))
> 
> 3 - Put the cursor -!- in the beginning of the s-expression
> -!-(load (expand-file-name "~/.quicklisp/slime-helper.el"))
> 
> 4 - Try using `C-M-SPC` or `C-M-@` to achieve mark-sexp. It does NOT work 
> (and it should work).

I cannot reproduce this in Emacs 26.3.  If, after step 4, you type
"C-h l" (that's the letter ell, not the digit one), what do you see?