Photos on Mac Catalina
Where is photo stream on new Mac?
iMac Line (2012 and Later)
Question marked as
My Photo Stream is not shown in Photos 5.0 on Catalina, if iCloud Photos is enabled. Then it is not possible to enable My Photo Stream as well. The My Photo Stream photos will be included in the All Photos album and not shown in a separate My Photo Stream album.
If you are using a new, recently created AppleID, you cannot enable My Photo Stream at all. It is only available for users with an older AppleID. The Photos user Guide for Catalina does not mention My Photo Stream any longer. Use iCloud Photos to store photos in iCloud - Apple Support