Stop apps opening on their own when you log in

A Mac you have owned for a year takes longer to become usable than one out of the box, and the reason is nearly always the same: a queue of apps opening behind the desktop the second you log in.

Go to System Settings → General → Login Items & Extensions. The first section, Open at Login, is that queue. Select anything you did not put there on purpose and click the minus button under the list. The app stays installed; it simply stops launching itself.

Below it sits App Background Activity, which is a different animal: helpers, agents and updaters that never show a window. Some of them earn their keep — printer drivers, backup software — and each one tells you which app installed it. If something you removed from the login list keeps coming back, this is where it is being relaunched from.

The payoff is immediate. You log in, the desktop is there, and nothing is fighting you for the disk for the next two minutes.

On macOS Sequoia, that second section is called Allow in the Background.