Describe the bug

To quote @carolinan:

When editing the site I found the Cancel text next to the Apply button confusing. I thought it would cancel the changes I had just made to the site templates and restore the previous state. Instead I was taken back to the single post editing.

And to quote Brent who commented in the call for testing (couldn't find GitHub username):

Its not clear to me when you edit the template if “Cancel” means “Discard my changes” or “Keep these changes drafted but don’t publish them yet”. There’s also some confusing about leaving when you haven’t actually made any changes. The “Apply” button doesn’t make much sense when you haven’t made any changes. “Cancel” could maybe be “Return to Post” or something when there’s nothing to actually cancel out of.

To reproduce
Steps to reproduce the behavior:

1. Install Gutenberg 9.6+ and a FSE ready theme.
2. Go to Posts > Add New
3. Make some changes to the post > Save Draft or Publish.
4. Use the option to edit the template to switch into template editing mode in the post settings section.
5. Make some changes to the header, footer, and post content.
6. Click "Cancel" as if you want to remove these changes.

Expected behavior

This is a bit unclear and why this issue is being opened. Does it mean remove changes? Does it mean "take me back to edit the post"?

Editor version (please complete the following information):

• WordPress version: 5.6
• Does the website has Gutenberg plugin installed, or is it using the block editor that comes by default? Gutenberg
• If the Gutenberg plugin is installed, which version is it? 9.7

Desktop (please complete the following information):

• OS: MacOS
• Browser: Chrome
• Version: Version 87.0.4280.141