I need to write a name that uses accents (original name is in French). I have seen the instructions. Go to Insert, then to Symbol, and a pop-up should let me choose the special character.
But "Symbol" is not listed under the "Insert" menu. So is there more than one "Insert" menu, and if so, where is the one I need to get to the "Symbol" so I can click on it to get the pop-up?
It sounds like you have the "new editor" in Confluence, where symbols are no longer offered. The instructions you're reading about the Symbol menu refer to the "legacy editor".
You can still include accents and symbols, though -- by using the features in your native OS. In this post about the new Confluence editor roadmap, it's noted that there are no current plans to reinstate Symbols since "symbols natively available through your OS are more comprehensive"
If you're a macOS user, here's an article from Apple that includes info on how to type accented characters.
Here's another Atlassian article that you might find useful that outlines the changes in the new Confluence editor.
I hope this helps!