Can I make a <button> not submit a form?

The default value for the type attribute of button elements is "submit". Set it to type="button" to produce a button that doesn't submit the form.

<button type="button">Submit</button>

In the words of the HTML Standard: "Does nothing."

The button element has a default type of submit.

You can make it do nothing by setting a type of button:

<button type="button">Cancel changes</button>