Open a collection that has four or more links.

Click on the last one, it gets highlighted as you would expect.

Now shift+click the one above it, it doesn't get highlighted, it gets "checked".

But all the links above it also get "checked" (why?)

And to make things even more confusing, the first link you clicked is highlighted but UNchecked.

I've been using Raindrop.io for years, and I still don't know how selection works.