backup for large files

1. It's not a file. It's a package - and that's just a folder set to look like a single item. It does this to protect the contents
2. The best way to back up a Photos Library is to copy it to an external drive formatted Mac OS Extended (Journaled) or APFS. Using an app that does incremental back ups is more convenient. Redundancy - that is, multiple back ups - is advised.
3. There really is no good remote back up for a Photos Library. Why not? If you try back up online the servers that the library might sit on will not be appropriate for the Library (i.e not formatted Mac OS Extended (Journaled) or AFPS) and so there is a real danger of silent corruption to the library.
4. However, it is perfectly possible to back your Photographs online and among the best and least expensive ways of doing this is with sharing sites like Flickr or SmugMug. These will protect your photos and also allow you to access them from any computer in the world. Other apps such as Adobe's Lightroom have this feature built-in.
5. The iCloud Photo Library is a sharing service, not a back up.

Some photo sites, such as Flickr and Smugmug offer apps that serve as uploaders, some can be accessed via the Share menu and, ultimately, any photo can be exported via the File -> Export menu item.