System Settings → General → Login Items & Extensions is the Startup tab. Two lists:
- Open at Login: apps that start with your session. Select one and press − to stop it, + to add one (or drag an app in). Right-clicking a Dock icon → Options → Open at Login does the same.
- Allow in the Background: helpers that run without a window, updaters, menu bar tools, sync clients. A switch per item; macOS adds a line here every time an app installs one, with a notification.
Windows also reopen: when you log out with apps running, the same apps come back at the next login. That is the tick box on the log-out dialog, "Reopen windows when logging back in"; untick it once and macOS remembers.
The impact column and the delay-start tricks of the Windows tab do not exist; the list is short by design, and Activity Monitor shows what actually costs energy.