Strikethrough text

I may be wrong, but it seems to me that there used to be a command in Apple Mail format to apply strikethrough. In any event, I want to use it again, but I can't find anywhere where it appears. I have been some references to BBc coding, but I don't want to have to learn how to use that unless I must. I want to keep it simple. Could it be that I saw, and used, this tool only on certain websites?

Another thing: Is there a way, or an app, that will allow me to apply tools like the ones in Apple Mail to typing anywhere? I suppose I can apply these tools in Notes and then copy and transfer my message elsewhere, but it would be simpler if there was a sort of universe toolbar to use any situation.