I have this error ( Notice: PageSettings\Manager is deprecated since version 1.6.0! Use Core\Settings\Page\Manager instead. in )
Even we change it to core\settings\page\manager. get_page() method is not available. ( undefined )

We did like your doc.
https://postimg.cc/image/gxqf15ezb/

I am not sure if it's related to v 2.1. I will create a ticket.

Any solution for it to get post id?

Thank you,