How can I back up my Photos library with iCloud?

Right, but it's precisely the iCloud library that I want to back up. Having to export, switch libraries and re-import every time I shoot new photos is not a viable solution for me. I rely on sync, I'm looking for a solution to back up "non-optimized" (full size) versions of my iCloud Photos while retaining the benefit of iCloud sync.

I keep my Nikon-shot photos in a separate library on an external drive, however when I open Photos settings with that library mounted, I get the window shown in the screenshot below. This is why I said it was a "system setting".

More precise terminology would be "setting of system library".

So I'm still without a solution, aside from buying a new laptop with more storage, or buying a non-portable computer with larger storage or that can stay permanently connected to an external drive. Both options feel like swatting a fly with a sledgehammer. I have several other Macs at my disposal, however believe all have "aged out" of iCloud sync due to incompatibility with the newest Mac OS.

Seems like this is the best idea: to create a second library which contains all photos through 2023, which resides on external storage, which can be backed up when attached, and keeping photos from 2024 through present on my devices synced through to present, not optimized, and backed up full time.

The other option I discovered, but which requires more intervention, would be to make a second user, which maintains a non-optimized Photos library, which resides on an external drive. As long as this user is running and the external drive is attached, and included in my backup plan, it also works (as would buying a second computer to stay online and synced with full size iCloud Photos).

I think Richard’s solution is safer and more elegant, it just means I won’t be walking around with my entire library on my daily drivers. I can probably save some money on iCloud storage now as well. If I keep the external library on a network share, access ends up being as simple as changing libraries (connecting via VPN if not within said network).

Thanks for helping me sort through the options Richard.

Thanks. Problem is, “optimize” Photos library is a system setting. I’m not clear how I could keep that setting on while initiating a second (non-optimized) library on an external drive.