What does the novalidate HTML attribute do?

Adding a novalidate attribute to the form element prevents native validation on form elements (if applied), allowing your JavaScript unobstructed ability to manage all validation

Based on the HTML5 course on Linda:

The novalidate attribute prevents forms from running their validation
logic when the form is submitted. In other words, it always lets the
form submission process go through regardless of what the results of
validation logic would normally.Now why would you want to do some like
that? Well, one main use of this is to allow a user to save a form’s
state so they can continue later without having to first validate all
the entries.

So if your web site, for example, is having a user fill out a form and
the user wants to be able to save their progress, you can disable your
form’s validation laws, and let them submit the form and continue on
later without having to force them to validate everything first

There are two attributes actually that enforces behavior. If you want
to use novalidate directly on the form tag, you can use the novalidate
atrribute right on the form itself.You can also do this on per control
basis.