"Is there another way around the iCloud deletion sync/Error"
The deletion across devices is the intended behavior of iCloud. The main purpose of iCloud Photos is to keep your Photos Libraries in sync and identical on all your devices that are syncing with iCloud Photos. If you not want identical libraries (less photos in iCloud and on your iPhone) stop using iCloud Photos, see: Three Good Reasons for Using iCloud Photos Library and when not to use it - Apple Community
To save your photos on your Mac before deleting them from your iPhone and iCloud you could simply duplicate your Photos Library on your Mac. That will work, if your Photos library on your Mac is containing all original image files- if you have not been using the "Optimize Mac Storage" feature for iCloud Photos on your Mac.
- Quit Photos, if it is running.
- Select your Photos Library on your Mac in the Finder, right-click or ctrl-click it and use the command "Duplicate" from the contextual menu.
- Now double-click the duplicate of the library to open it in Photos. You may see a message about "Restoring Library". Wait until this has finished.
- If Photos is giving a message about "incomplete items" not all items have been downloaded from iCloud. You have to ensure, that all items are stored locally by viewing all photos enlarged or playing the as a slideshow or similar, before you duplicate the library.
"This file type is either not compatible or does not have valid information"
This error message is typical, if you try to import sidecar files, like :XPM or .AAE files separately to Photos. These files are not image files and cannot be imported separately. Photos will import them automatically, when we import an image or video with the same name from the same folder.
You may also be seeing this message, if the Photos Library is stored on a volume with an incompatible file system format. Make sure, your Photos Library is stored on a supported volume, if you are keeping it on an external drive. Move your Photos library to save space on your Mac - Apple Support
