You have been incredibly helpful in helping me to understand the logic and arrangement of the albums that Apple makes available on all my devices through iCloud Photo Library. I am beginning to understand how to make use of what I have. It appears the "All Photos" is no longer available on my iMac and I will not miss it since the Photos selection within the Photos Library is what I want. I like the clean, uncomplicated presentation of all my pictures together with the date grouping shown at the top of the screen.
My IOS devises still have All Photos which give my preferred presentation but I now understand that I can get to my preferred order of pictures (picture taken date/time). I just cannot get that preferred order of pictures in the clean presentation that my iMac provides. Maybe someday the clean presentation and preferred order of picture taken date/time provided by the Photos selection within Photos Library on my iMac will also be available on my IOS devises. On my IOS devises within Photos I have the three selections Moments, Collections and Years, just not the fourth selection, Photos. This fourth selection that my iMac has Photos within Photos is the selection that I most prefer.
Again, many many thanks for all your help. I believe I have come a long way in understanding what I have available to me.