The automatic turning on is definitely a setting you would need to have turned on.

Do you have multiple Apple devices? You might have set them to mirror each other so they all share the same focus mode.

You might have created a shortcut that is attached to an automation to turn it on based on some trigger, (time, place) etc.

Or in the focus mode settings you can click on do not disturb and it should list how it is set up.

On the do not disturb settings page under focus, near the bottom is “on a schedule”.

You can have a time schedule, as well as a smart activation, where it tries to learn when to do it automatically.

For instance gaming focus has learned to turn on when o play a game for like 5 minutes.

If you turn those off and ensure you don’t have an automation in the shortcuts app that turns it on, you should be at only manual control.

On projects I setup I have prettier run as part of a commit hook. All files will be formatted at all times