Steps to reproduce:

Install clean version of DXP v4

Go to a landing page content and click on "edit"

Add a Text Block to the landing page (dont publish) 

Click on Block Settings icon

Remove the default Text Block name which is Text and sumbit, you will get a required field message

Now click on Cancel button, you will notice that it does not work. (works on DXP V3)

Expected result:

The Cancel button must allow to close the block.