how can I pass in additonal arguments like -w, -s

[it6]

how can I pass in additonal arguments like -w, -s

[dajva]

Spaces are escaped to allow for search terms with spaces in them. This comes from emacs builtin read input functions.
If you don't want to use type C-u every time you can define your own wrapper:

(defun my-rg ()
  (interactive)
  (let ((current-prefix-arg '(4)))
    (call-interactively #'rg)))

[dajva]

rg-command-line-flags is a global variable so it's suited for flags you want in every search.
It's customizable by doing M-x customize-group RET rg RET and adding flags under the Rg Command Line Flags setting.

If you want to add a flag for a single search you can use the prefix argument C-u to the rg command. That will let you edit the full command line before it's executed.

[it6]

I see a \ being added to the -w flag when I try to add flag without using C-u this is causing the search to fail is there anyway we can enable this feature without pressing C-u

This throws an error as mentioned above

rg --color always --colors match:fg:red --type less --no-heading --type-add 'gn:*.gn' --type-add 'gn:*.gni' --type-add 'gyp:*.gyp' --type-add 'gyp:*.gypi' -i -w\ onboarding

This works as expected

rg --color always --colors match:fg:red --type less --no-heading --type-add 'gn:*.gn' --type-add 'gn:*.gni' --type-add 'gyp:*.gyp' --type-add 'gyp:*.gypi' -i -w onboarding