This is an area that Apple hasn’t tackled just yet.
If you want to share your entire library with someone (like a spouse/partner), Google makes it easy. Click the hamburger icon on the iPhone app.
Type in the Gmail address of the person with whom you want to share your library.
On this final screen, you can choose what you want to share. This can be only photos of certain people (it uses face scanning), only photos from a certain date onward, or everything. When sharing a library, that person won’t be able to make new albums or see your automatic creations. They will simply have a feed of all of your photos.
For families, family sharing is a great feature. I expect Apple to adopt something similar for iCloud Photos in the future.