Since more than three years there is a warning in many Apple Support documents, that users with a new Apple ID may not be able to activate my Photo Stream at all, for example: (If My Photo Stream isn't updating – Apple Support (UK))
" If you've recently created your Apple ID, My Photo Stream may not be available. Use iCloud Photos to keep your photos and videos in iCloud. Find out more about iCloud Photos and My Photo Stream."
The writing is on the wall. It looks like Apple were keeping My Photo Stream alive, just barely, for the sake of long term users with older devices, that cannot be upgraded to support iCloud Photos or the manual syncing with the Finder instead of iTunes. All upgrades to iCloud are only available for iCloud Photos - a true syncing of all edited adjustments and metadata, support for Live Photos and videos and HEIF, a long term storage of media files, not just a temporary storage.