View: Toggle Menu Bar in Title Bar
view.toggleExtendedWindow Draw the menu bar inside the window's title bar instead of below it (experimental; not available on macOS; applies on restart).
How to run it
Open the command palette (M-x in the Emacs keymap) and search for View: Toggle Menu Bar in Title Bar, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.