Name your regex better

[otajor]

Your regex here should not just be called regex. That doesn't give me as a code reviewer a lot of extra information.

It would be much better if you isolated it in its own function with a good name e.g.

function isSpecialCharacter(string) {
  return string.match('[?<>=+()*&^%$£@!#:;``~{}\[|_\\\]]')
}

form.addEventListener('keypress', function(e) {
  if (isSpecialCharacter(e.key)) {
    e.preventDefault();
  }
});