Below found in the wild expanding a macro from Daniel's marginalia package.

Emacs 30

(macroexpand-all '(foo bar)) -> (foo bar)
(macroexpand-all '((foo) bar)) -> ((foo) bar)

master

(macroexpand-all '(foo bar)) -> (foo bar)

(macroexpand-all '((foo) bar)) -> signals an error

Debugger entered--Lisp error: (wrong-type-argument symbolp (foo))

  signal(wrong-type-argument (symbolp (foo)))
  function-get((foo) compiler-macro)

Whether this is an intended or unintended consequence, I can't say, not being a macro expert.

-Stephane (and Daniel)