I want to add a new tab to the phpBB forum main menu, for example in the main menu on the top bar next to Forums. I am using the elegance theme (artodia.com).
I suggest making an extension for it.
Specifically you are looking here
https://github.com/phpbb/phpbb-ext-acme-demo/blob/master/styles/prosilver/template/event/overall_header_navigation_prepend.html
Total_header_navigation_prepend event
If you download the linked repository you can also create the master page
