To share a link to the current page and add annotations to it is now a matter of just one click.
No need to open the annotation sidebar anymore.

Just press alt+y on Windows & Linux or option+y on Mac to get started or use the "Share Page" button on the action bar.

Important note:

Mind that this just creates the link, you still need to add annotations to it.
If you already made annotations on this page and wonder why there are none showing up, this is because all annotations you make are by default private and not associated with a Space or page link.

So you got to either go to the "My Annotations" tab and add them to the page link by clicking on the + icon, or create new ones while you are in that initial view, where all new annotations are automatically associated with that link.