“I’m fine” is a lock on a door, not a description of the room.

Two words can close a conversation without telling anyone anything. They are useful, and usually the usefulness is the whole point, since not every person or moment has earned the longer answer. The trouble starts when the short version becomes the only one available, including to people who would have sat with the long one.

Notice who you say it to this week and whether any of them would have stayed for more. Pick one and give a slightly truer answer, even a plain sentence about being tired or worried. You keep the lock, you just use it on purpose.