Photos

You could split your Library into two or more smaller Libraries. I would do this by duplicating the Library then deleting complementary parts from each of the duplicates, perhaps by date, perhaps by theme depending on how you work with the pictures. I have two Libraries, one for work activity and one for private.

Stephen

I agree that a bigger drive is the best answer. However, my approach does not take up more disk space.

Take your Library L and duplicate it. You now have L1 and L2. From L1 delete everything before, say, 2015; from L2 delete everything from 2015 onward. L1 and L2 are now half the size they were and together roughly the same size as the original L, which can be deleted. (I've just realised I didn't mention that bit in my original post - sorry!)

You can now move L1 or L2, which should help with the original question "Is there a way to load as much as possible before getting a new hard drive?"

Take your Library L and duplicate it. You now have L1 and L2.

So immediately you require twice the disk space.

From L1 delete everything before, say, 2015; from L2 delete everything from 2015 onward. L1 and L2 are now half the size they were

So you're working on the only complete copy of the library? There's no contingency there if something goes wrong?

The theory is correct, but in executing it there's at least one point where you need a minimum of twice the disk space. I was assuming you'd keep one copy as a back up and work on duplicates.

Edit: a thought: using PowerPhotos it would be possible to create a new library on the external and move material to it, with no duplication. Though, again, it's not wise to do this without a back up.

https://www.fatcatsoftware.com/powerphotos/

When you get yourself a new hard drive for the library, get yourself two new drives. You will need the second one to keep backup copies of the moved library. If your current external volume should be your Time Machine volume, do not even think of moving the Photos Library there. Photos cannot work reliably with a library on a Time Machine volume in the recent versions of macOS X since macOS 10.13 High Sierra.

Power Photos is perfect for splitting Libraries, but limited in the older versions of MacOS X. It is only since macOS 10.15.4 that we can move photos between libraries with PowerPhotos while keeping the originals and the edited versions paired. On older system versions the method outlined by Stephen is the only way to split the library in a lossless way. macOS 10.15.4 has made it easier for third-party applications to work with a Photos Library. But even PowerPhotos on macOS 10.15.4 or later cannot split the library without copy errors, if you are using iCloud Photos and optimise storage. The photos need to be downloaded and stored locally.

Which version of macOS X is running on your MacBook? Are you using iCloud Photos?

Won't that process take up 2.5 times the disk space? The original, the duplicate, the one half?

Getting an bigger hard drive is the solution.

I agree with you, Terence, although I'd assumed there was a backup process somewhere in the setup.

Yes, my first thought was PowerPhotos, which seems to me to be a better application than Photos.