Probably you don't have local user
$MYVIMRC is pointed to the one that was used to initialize your vim. If there is no user
.vimrc it would be system-wide one and usually you would have to edit it with superuser rights.
So in vim, do
:e ~/.vimrc and add your settings there. Bear in mind there is also
:h defaults.vim) that is loaded if there is no user
.vimrc... meaning you wouldn't get all the things from there unless you add them explicitly.
PS, better place for your settings is a
~/.vim/vimrc if you plan to store you config on a github/gilab/whatever.
PPS, you have added
vimrc file to a
vimfiles/vimrc/ folder and it should be
II The user vimrc file(s):
"$HOME/.vimrc" (for Unix) (*)
"$HOME/.vim/vimrc" (for Unix) (*)
"s:.vimrc" (for Amiga) (*)
"home:.vimrc" (for Amiga) (*)
"home:vimfiles:vimrc" (for Amiga) (*)
"$VIM/.vimrc" (for Amiga) (*)
"$HOME/_vimrc" (for Win32) (*)
-----> "$HOME/vimfiles/vimrc" (for Win32) (*) <----- HERE
"$VIM/_vimrc" (for Win32) (*)
"$HOME/config/settings/vim/vimrc" (for Haiku) (*)