Ok so I think there are several misunderstadings here.
First, option+s, you probably have it bind so something in your vault or maybe it is some plugin that took it. That’s why it doesn’t work for you. You can look at your hotkeys or delete .obsidian/config and start fresh.
Second I don’t hink that ctrl-p and ctrl-n have been implemented by codemirror for autocomplete.
https://codemirror.net/keymap/vim.js
They are just remapped to j k.
You can ask suggestions about vim mode in these threads
https://forum.obsidian.md/t/support-loading-vim-commands-from-configuration-vimrc-style/5826/
https://forum.obsidian.md/t/vim-mode-quality-of-life-improvements/429/