How to output ALL of the settings an Emacs version comes by default with as text to see where the differences between the versions are?

Question

The Title already tells what the question is about.

The purpose of the answer to this question would be to become able to find out which default values differ between the versions 27.1 and 28.2 of Emacs in order to set them explicit in the initialization file achieving as consequence the effect that the layout of the windows for both versions which currently looks like this:

will become the same.

Answer 1

Use emacs -q to launch Emacs, then use M-x ielm and issue:

(defun customizable-variable-value-pairs (&rest other-features)
  "Print all the bound customizable variables from the loaded packages and C source code, with their default values.

For those unloaded packages, you can pass them as the arguments so that the bound customizable variables from them will also be printed."
  (mapcar (lambda (feature)
            (require feature)) other-features)
  (mapatoms (lambda (symbol)
              (when (and
                     (custom-variable-p symbol)
                     (boundp symbol))
                (print (format "%s"
                               (cons symbol (symbol-value symbol))))))))

Here's an example:

(customizable-variable-value-pairs 'whitespace 'tramp)

PS: It is a long list.

to see where the differences between the versions are?

You can search, say "28.1", in the symbol's docstring to see whether that symbol's default value was changed in version 28.1, or that symbol was introduced in version 28.1, etc.

---

According to your question description, C-h n may be another choice:

C-h n runs the command view-emacs-news

...

Display info on recent changes to Emacs.
With argument, display info only for the selected version.

That's all you want.

For example, if you want to see the changes about themes, use C-s theme in the buffer NEW:

** New themes 'modus-vivendi' and 'modus-operandi'.