I found my self searching for that feature many times, I think it will be very useful for people making workshop or streaming for example!
Do you mean toggle the code? For me it works with CMD+/. But maybe we don't have proper bindings for Windows or something?
Oh! It can't work for me because my keyboard layout T_T
Would be awesome if added on the Keybinding section then?

Here in Norway—and probably many no-English countries—the / key is behind a modifier key. So ⌘+⇧+7 is required to comment which does work in vscode, but not Codesandbox.
I have the same issue with a Portuguese keyboard :(
You can override this if you are using vscode win codesanbox now
Closing this, as the key bindings can now be edited from VSCode:

@cloud-walker Feel free to reopen if you still have issues, though.
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You can override this if you are using vscode win codesanbox now