Example plugin code to add menu items under Main menu & System cog (Mautic 6.x & future 7.x support)

Hello Everyone,

I’m looking for a reference or example plugin that shows how to add:
* a menu item under the Main menu (left sidebar)
* a menu item under the System cog / Admin menu (top-right)
* buttons to the top of a menu page like the save, save and close and exit buttons etc

The goal is to create a plugin compatible with Mautic 6.x, and ideally future-proof (or easy to update) for Mautic 7.x.

To be clear:
* I am not asking anyone to write the code for me
* I am not looking to pay for custom development
* I’m just hoping someone can point me to an example or existing public source that already demonstrates this

Specifically, I’d appreciate pointers to:
* Correct `config.php` menu definitions (for both menu locations)
* Parent menu keys for Main + System menu sections
* Plugin file/folder structure
* Any permissions required so the menu entries display
* Notes if menu structures are changing between 6.x → 7.x

There is reference to such code on the forum back in 2021 however that must be very out of date by now and won’t support M6.x or M7.x.

If you know of a GitHub repo, documentation link, or open-source plugin that already implements this, sharing the link would be perfect.

Thanks in advance — trying to follow best practices and avoid reinventing the wheel!

Thanks