How to create an exit button? Previously found codes aren't working!

You could put this in place by having a button in the survey's Footer that sets an Embedded Data field and advances the page when clicked. Then, use Branching or Display logic to direct the respondent to the end of the survey if the Embedded Data field is equal to "true".

To give it a try, first create an Embedded Data field at the top of the Survey Flow called "exit" and set its value to "false".

Then in the Look & Feel, add the below to the Footer to insert a button:

<button type="button" id="exit">Exit</button>

Then add the below to the Header to turn the Embedded Data field "exit" to "true" and advance the page when the button is clicked:

<script>
Qualtrics.SurveyEngine.addOnload(function() {
jQuery("#exit").on('click',function(){
Qualtrics.SurveyEngine.setEmbeddedData("exit", "true");
jQuery("#NextButton").click();
}); 
});
</script>

Finally, add Display Logic to the rest of the questions so that they only display if "exit" is equal to "false". Or, add Branching to the Survey Flow after each page which directs the respondent to an End of Survey element if "exit" is equal to "true".