amenalum wrote: Simply wanting to sync pix from iPhone 15 to iCloud so I can back them up and delete them from the phone and save space.
I fear you don't quite get what iCloud is for. iCloud Photos is a synchronization service. When you engage iCloud Photos on a device, then the Library on that device is kept exactly the same as the iCloud Photos Library. So, for instance, if you take a picture with your iPhone, it is added to the iPhone's Photos Library, copied to iCloud Photos Library, and then copied to the Photos Library on each of the other devices that you have connected. If you delete a picture on your iPhone, then that picture is deleted at iCloud and removed from all the other devices. You say you want to "sync pix," but synchronize means "keep exactly the same."
So you can't think of iCloud Photos as an archive service or as a backup service, since it backs up deleting, even ti they are mistakes, and there's no way to undo them. Whatever you do with Photos on your device-- it happens exactly the same everywhere else. For archive or for backup, you need some external storage like a flash drive or an external drive.
To save storage space, you can use Optimize Storage on your iPhone. If you set a device to "Optimize Storage" in Settings>AppleID>iCloud>Photos, then Photos may store only smaller images on the device and rely on iCloud to keep the full sized images. This means you can quickly scan through all of your pictures any time. And if you want to magnify a picture to see more detail, Photos will reach out to iCloud to get a full sized image for you to zoom in on. It's the same for editing or printing or anything that demands the full picture. Your optimized Library may take up less than 20% of the space of a fully downloaded Library. But an optimized Library may be kept larger than that if the extra storage space is not needed.
So, you can't "sync pix from iPhone 15 to iCloud so I can back them up and delete them from the phone and save space." You can use Optimize to save space, instead.
By the way, Finder is the File Manager app for a Mac, kind of like Explorer on Windows.