The M is silent. In computing this stands for the underlined letters in menus that can be triggered using an Alt+Letter key combination, one that you can remember and apply later to navigate around more quickly.
That shutdown mnemonic in particular, has been driving me bonkers lately. I use it to restart. Is it alt+r? alt+e? will pressing alt+<underlined character> actually do the thing, or will it select the other alt+<same character> from elsewhere in the menu and start some application?
No, I haven’t reported this one yet. It keeps changing with every update, so maybe it’s really fixed already. IDK, there’s a queue and it ain’t at the front yet But It’s cool to see that it’s getting attention!