Thanks for writing us, the new share mode has been changed for better experience. You can now use the share tab option which located at top header next to prototype tab to share.your design And in order to invite to document click on presence icon present at right corner of the header and go ahead and share the document with other through email.
Please refer the this link for more info : https://helpx.adobe.com/in/xd/help/share-designs-prototypes.html
You can also refer the attached gif.
Hope this will helpful, if not please revert back. Happy to help you!!
I confirm what has been said by rreddy. The sharing mode has been moved to the top, in order to improve the user experience and have everything in the right place
It's so funny, to see how Adobe (like many other developers) tried to get rid of the good old menu commands bar. And eventually, after some detours and flawed ideas, they're returning to a bunch of key buttons in the top left area, spawning menus, drop down options, and other kinds of lists and panels, to facilitate certain features.
Menu commands weren't so bad... 😉