Sync Photo library between Photo application on two Macs using same Apple ID / iCloud account

If you are using the same apple ID/ icloud account, that is exactly what iCloud will do.

First check that the library is set as the system library - the circled button should be greyed out. (Photos preferences) If it isn’t, click it.

Then check icloud settings are as shown. If you don't have enought storage on the macbook for the full library, then select "optimise mac storagee" and only thumbnails and smaller previews will be permananently kept on the mac. Full size will stay in iCloud to be downloaded as needed (eg for editing/export)

Also make sure you have enough iCloud space for your whole library, and lots of free space on your mac and phone.

It is one of the best features of iCloud Photos that we can work with our photos and videos from multiple devices, different platforms, different system versions. it is nearly magical how seamlessly it is working across different devices. You cannot share the local Photos Library between your Macs, but you can certainly share the iCloud Photos Library. Set it up as described by Tony.

I am using iCloud Photos from four different Macs - two of them are using Photos 4 on Mojave, two are using Photos 7 on Monterey. And an iPad with iPadOS 15, an iPhone with iOS 15, a very old iPad with iOS 10.

It is working like this:

• iCloud Photos is storing our Photos Library in iCloud, in full quality.
• Each of our synced devices is keeping an own local copy of the Photos Library, formatted for the system version.
• When we work on one of our devices with the local library, for example import photos or videos, adjust photos, modify metadata, it will be synced to iCloud, the central Photos Library will be updated, and the changes will automatically be synced to all other devices.

Things to consider:

• At least one of your Macs should make regular Time Machine backups, so you will have a Time Machine backup of your iCloud Photos Library.
• The device with the least storage will be the bottom neck, determining how large your iCloud Photos Library can grow. The complete iCloud Photos Library will sync o all devices and take up storage on all devices. You can use "Optimize Storage" for the device with the least storage, but optimisation cannot remove the local data completely. You will deed at least enough storage for thumbnails and previews. As an estimate - if your Photos Library has a size of 250 GB, the optimised version will require at least 25GB, with 50GB it would be more responsive. Plan your iCloud Photos Library to need no more storage than the storage 5 times the storage you can afford for photos on the device with the least storage.

Great that is is working for you now.