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.
https://superuser.com/questions/110605/how-do-i-type-accented-characters-in-windows lists a couple of solutions, but personally switching to a Polish keyboard layout on Windows seems to be the best solution. I followed https://polishlingo.com/2017/08/30/how-to-type-polish-letters-in-windows-10-on-your-english-keyboard/ and could type ś by pressing Alt Gr + s. Even here in Discourse.