You cannot directly share images from Lightroom Desktop to Photos App.
You need to first export the images from Lightroom desktop and then, import in the Photos application.
thanks for the quick reply, so how come we can do it on the iPad!
There is no direct interaction between Photos App and Lightroom on desktop.
How exactly are you doing it on iPad?
go to share thingy
select open in
select iCloud photo sharing
post in (album of your choice )
jobs a good un.
Yes, iCloud sharing feature is available only in Lightroom Mobile, not in desktop version.