Microsoft Dynamics 365 team has been transitioning all documentation to the new docs.microsoft.com site and just launched now is the new documentation for portals. This is a great change to see and is starting to bring the breadth of documentation in alignment with what is available on the legacy Adxstudio Community site. Having it in the Microsoft docs site will help make the content much more accessible and easier to refer to in blogs, forums and all other ways of sharing :).
The documentation is still a little short on the newest components that are available (no chart liquid object and a couple other items) but I look forward to this being continuously updated as new releases come out. This is only the first release of the documentation and I think we can expect it to be updated regularly.