[Solved]-How to see if a user has clicked off a TextField in MUI-Reactjs

You can listen to onBlur event.

const handleOnBlur = (e) => {
    alert("Left text box with the value: " + e.target.value);
};

<TextField
        onBlur={handleOnBlur}
        id="outlined-basic"
        label="Outlined"
        variant="outlined"
/>
 

Note: If you want to fire POST request whenever the text changes, you can read about debounce

Refer: Perform debounce in React.js