Reply to MrHoffman.... in Q? order:
A. Operating systems of each device Oct 3d, 2019
iPhone XsMax (512g capacity) 13.1.2
iPadPro12.9/3d gen (1 T capacity) 13.1.2
iMac Retina 5K 27" Late 2015/i7 ( 3 T capacity) 10.14.6
B. iCloud backup is not what I was confused by. It was supposed to be to access my photos from ALL DEVICES equally. The fact is, the wording of the Options for iCloud photo storage allows me to keep the backup of photos on my iMac, as long as there is room (which there is).......so I have the entire Photos of 14,000 + on the iMac. I also keep the original photos taken on the iPhone available on the iPhone. I do so because of the great apps for that operating system.
The apps I've tried to use on iMac to edit my photos there do not want to access the Photos.app,.....they want to access the iCloud/PICTURES/Photos.app..... but my Photos.app is not accessible via PICTURES.....through that route, only FOUR PHOTOS are accessed, for whatever reason.....and that confused me, because it has been this way from the first Apple device that I got.
C. I have Time Machine, first backup, with a second backup on a 2bay Seagate.
D. Yes. Photos.app is part of macOS, and that is where my photos wind up regardless of the camera used. I use it.
HOWEVER, these 3d party photo editing apps (from the AppStore) assume the Photos.app is nestled within PICTURES but it is NOT THERE.
E. When I log in to iCloud via Safari, and check Photos there? AHA.....there I see all of my Photos just like on the devices, including on the iMac......hmmmm, that does not help me with enabling the app I wish to give access to my Photos.app though, because it wishes to go through the PICTURES folder of the iMac.
This particular way of accessing my photos on iCloud is new to me, and I thank you very much for helping me make the connection with it. Since I began using Apple products in mid 2015, I have never known how to access the site in this way. From my iMac direct to the iCloud, I do not see any of these folders, like Mail, FindMyiPhone, etc......and a big dread is no longer darkening my thoughts!
F. I'm not able to use Photoscape, although I downloaded it from the AppStore. Because it will not allow me to use Libraries, and the setup requires I go through PICTURES to reach PHOTOS.APP......and of course, not possible for whatever reason.
G. I'd love to have a "local Apple Store" but none is within 150 miles of here, New Orleans has one. Mobile AL has an authorized repair person, not an Apple Store. I can only wish!
I will correct my thinking and try again, perhaps contact the Photoscape.app developers for a workaround. Never have contacted a developer, so that will be a learning experience too!
Thanks for your input. I'll update my response if/when the problem is resolved.
BJ