Date: Mon, 21 Mar 2022 15:41:57 +0100
From: Andreas Röhler <andreas.roehler@easy-emacs.de>
C-h k RET tells
[...]
Insert a newline, and move to left margin of the new line.
----
"Left margin" is not the case from Emacs -Q, where it indents that newline.
The doc strings says more than that. It also says:
If ‘electric-indent-mode’ is enabled, this indents the final new line
that it adds, and reindents the preceding line. To just insert
a newline, use M-x electric-indent-just-newline.
And if you evaluate electric-indent-mode, you will see that it is
enabled in your case.