Tab 99 is not an option for a new Tab anymore?

This hasn't been changed in a while. Tab 99 can be opened with Tab + number or in the browser from the Setup section.

But is there a special reason that it is no longer listed in the "New-Tab-Window"?

Thanks for the hint with the Setup Section. I never would have found that, nor would have looked in this place.
I somehow didn't read the release notes propperly.

I don't remember ever seeing it in the main "add a tab" listing. 

I am very sure it was. Because this is how i found it.