iMac using iCloud Drive?
Why do you want the photos in the cloud instead of on a local drive? I understand, if you do not want external drives connected to a laptop computer that you keep carrying around, but for an iMac sitting on your desk a local, external drive is preferable to a cloud storage for photos. In the long run it is much less expensive, your photos will always be available, even if your internet should be slow or not working, editing and browsing will be faster. There will be less risk of data loss by transmission errors.
And you will be in control of your photos and not depend on others to store them. Making backups to keep them safe will also be much faster - simply include your drive with the photos into your regular Time Machine backup or make a clone of the drive with the photos.
Cloud storage for photos on a desktop computer will make sense as a secondary storage, if you want additional copies of the photos offsite as an added backup, but not as the only storage of your photos you want to be working with. Why get yourself a fast, expensive computer, if you slow it down by having to download large media files from the cloud whenever you want to work with them? I keep the originals of the photos on a second internal drive.