Photos Library Showing Zero Bytes on Mac Finder but photos are intact

This is the system photo library in the photos app.

How have you checked this? Photos may be using a different library from what you are thinking you are using.

Just to be sure about the location of your library, launch Photos. And when you are seeing all photos, go to the Photos > Preferences > General and look at the path to the library at the top of the panel. Click the first folder icon after "Library Location" to see its name.

Then click at "Show in Finder". Is this showing the library with the zero bytes or a different library?

Which system version do you have installed? The trouble with a library size shown incorrectly started with macOS 10.15.1, but the system version below your question is showing macOS 10.14, where the Finder has still been showing reliable library sizes.

You have been asking about iCloud. The library may not contain all photos, if you are using optimise storage. Then some of the older photos may habe become replaced by smaller, opted versions and only be saved in iCloud in the full resolution. If you are using the option "Download Originals" instead, the library should contain all photos and will be roughly 20% larger than the total size of all photos in iCloud.

If you want to backup your photos with Time Machine, do not use "optimise Mac Storage" for iCloud Photos but "Download Originals".

Hi

It seems to be a common bug with photos libraries that the size is not updated. It is not actually a single file, but a so called package which is like a folder with subfolders and files.

It seems to be quite common for the top level package not to have its size updated when the folders/files within are updated.

If you want to check, you can right click on the library, and select "open package contents". You can then check the size of the internal folders "originals" and "resources".

DO NOT CHANGE anything in the package using finder. If you do you will likely damage your library, potentially stopping it working and losing access to your photos. It is safe just to do a "get info" on the subfolders however.

Your other option is to copy (not move) the library to an external drive, and see if the size of the copy is shown correctly.

While Photos is uploading 30000 photos and videos, it will not start downloading missing photos, so you will have to wait a bit, before the Time machine backup can include all photos. But it does not hurt to start with Time Machine now, as it is making incremental backups. You will at least be saving, what can be saved now already.