What problem does this address?

In the new template management feature added in WordPress 6.9, to edit a theme template, you must duplicate the template as a "Created Template" and then edit the duplicate.

Up to WordPress 6.8.3, clicking a theme template opened the template edit screen. However, in WordPress 6.9's template management, only the "Copy" option appears, which may confuse users accustomed to the previous behavior.

What is your proposed solution?

Therefore, how about adding a lock icon similar to the pattern icon?
This would implicitly convey to users that theme templates cannot be edited.

Reference
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