Images are not showing up at full resolution using Photos for Mac

I understand your frustration with the resolution issue in Photos for Mac. While I can't provide a specific solution as my knowledge is based on information up to September 2021, I can suggest some general troubleshooting steps and potential workarounds that might help improve the situation. Keep in mind that software updates and changes could have occurred since my last update, so it's a good idea to check for the latest information from Apple and the Photos community.

1. Update macOS and Photos: Ensure that your macOS and Photos app are up to date. Apple regularly releases software updates that may include bug fixes and improvements.
2. Check Photos preferences: Open Photos and go to "Photos" > "Preferences" > "General." Ensure that "Download Originals to this Mac" is selected, and not "Optimize Mac Storage." The latter option may store lower-resolution versions of your images on your Mac to save space.
3. Check iCloud settings: If you're using iCloud Photo Library, go to "Apple menu" > "System Preferences" > "iCloud" > "Photos" and verify that "Download originals to this Mac" is selected. This step ensures that you have full-resolution images on your Mac rather than relying on the cloud versions.
4. Check storage space: Ensure that you have enough storage space on your Mac to accommodate the full-resolution images. If your drive is nearly full, it may cause issues with image resolution.
5. Rebuild the Photos library: Sometimes, issues with resolution or image appearance can be fixed by rebuilding the Photos library. To do this, hold down the Command and Option keys while opening the Photos app. You will see a prompt to repair or rebuild the library. Try rebuilding it and see if it improves the resolution problem.
6. Check Smart Previews: Photos might be using Smart Previews instead of the original RAW files, which could affect the image quality during editing. To check this, go to "Photos" > "Preferences" > "General" and make sure "Use RAW as Original" is selected.
7. Use a different image editing app: If the resolution issue persists, consider using a different photo editing app like Affinity or Luminar for your initial review and editing. These applications might handle RAW files and resolution differently than Photos.
8. Seek help from Apple Support: If none of the above steps help, it might be worth reaching out to Apple Support for personalized assistance. They may be able to provide additional guidance based on your specific setup.

As a general precaution, it's essential to have backups of your photo library before making any significant changes to the software or library structure. This way, you can restore your photos if something goes wrong during the troubleshooting process.

Remember to keep an eye out for any updates or bug fixes from Apple that might address the resolution issue. The community bulletin board you mentioned could also be a valuable resource to stay informed about potential solutions and workarounds from other users experiencing similar issues.

I am finding this issue frustrating as well. Images imported as Nikon RAW show up in high resolution in the full preview screen. Once "edit" is clicked on the preview screen it also shows in proper high resolution and can be zoomed as you edit. Once the edit is saved it shows only a very low resolution image (possibly thumbnail) in the Preview window which cannot be zoomed.

With some experimentation I found that if you open an image that has not been edited and paste a previous edit setting using "Copy Edits - Command-Shift-C" and "Paste Edits - Command-Shift-V" the image resolution is reduced immediately. If, after the image resolution has been downgraded, you then select "Revert to Original" from the Image Menu you can apply that same edit using a shortcut (Command-Shift-V) rather than using the "edit" button and the image resolution is preserved in the Preview window, even when you scroll back and forwards to previous or next images. This new edited RAW image resolution is preserved along with its edits and the full, zoomable resolution even if you quit the Photos application and come back to that image later (which is not the case for images that are altered after pressing the "Edit" button on the top right of the preview window).

So it appears that there is corruption being applied in the edit process that forces the application to only use a thumbnail resolution image in the Preview Window. Why it works when applying it to an image reverted to original is unclear. This is not a fix, and the frustration remains - because the process of editing an image, copying the edits, saving o return to the Preview screen, reverting to original and then reapplying the edits using a shortcut is crazy and time consuming. But it might help someone track down the problem a bit quicker.

I would love to know what the problem is once a fix is posted or released.

in your original post you are mentioning, that you are using a NAS to backup your photos. The NAS will be fine to backup image files, but you must not store a Photos library there and open it while on a NAS. Photos has not been designed to work with a library on a NAS; if you try it nevertheless, the library might get corrupted silently in the background, and you may notice it only when it is to late.

Is the system version stated below your question still valid? macOS 10.15? Or have you upgraded to the current system version macOS 13 Ventura? Are your photos RAW files?

I am asking because the current problems referred to in the post of YerMan are primarily occurring with RAW images on Ventura.