I assume you are using Windows. Does Alt Gr + s work for you in Notepad? It doesn’t work for me as long as I am using an English keyboard layout.
keyboard - How do I type accented characters in windows? - Super User lists a couple of solutions, but personally switching to a Polish keyboard layout on Windows seems to be the best solution. I followed How to type Polish letters in Windows 10 on your English keyboard | Polish Lingo and could type ś by pressing Alt Gr + s. Even here in Discourse.