tasky | : wrench : Useless overengineered powerless command line

Your solution is the correct solution and does indeed improve the accessibility for keyboard users.

If you need some reassurance check the W3 examples for a flyout menu

Much better than tabindex="-1" would just be to add display: none via a CSS class and change the menu item to a (assuming the top level menu item is not a link). Then opening the menu is as simple as toggling the CSS class and avoids any potential errors with managing tabindex.

If the top level item is a link to another page then follow the principles of option 2 and have an additional drop-down icon next to the main link instead (with aria-label="open (menuItemName)" for example).

The final consideration is that once a menu is open that is a "mega menu" style (multiple columns), you should ideally implement arrow key navigation to take you between columns and items.

As for whether pressing Tab should go to the next top level item it is something that I am not sure if there is any guidance on, I personally say yes it should and arrow keys are for navigation within a drop-down, but I would make it a true drop-down with aria-owns on the

If you have the knowledge of how to implement WAI-ARIA correctly then that is the best option, if not then making the Esc key close the mega menu and or pressing "up" when at the top of the list to get back to the top level links is a reasonable compromise.

I do have one other thing you can do straight away (I know sometimes there is not the scope to fix things right now) as a stop-gap "solution".

Add tabindex="1" to the search box so it is the first item that receives focus and make sure you have "skip to content" links so people can bypass the menu.

While this certainly does not solve the issue, it does improve accessibility / UX for keyboard users in the short term while you fix the problem, and although it doesn't follow "logical focus order" it would be a better experience (as a temporary fix).

Something that you can do quickly while you explore a more robust solution to the mega menu with arrow key functionality etc. etc.

I will stress this point one more time, this is a temporary improvement, not a fix!