First of all, whoever just upvoted this - thank you! (it reminded me to come back to this and resolve it)

The solution (now) is simple - use the latest version of RealmSwift

Notice the url in the "Location" column. That's all you need.

Delete whatever you are using that doesn't work.

Starting fresh, use the url:

"https://github.com/realm/realm-cocoa.git" 

and accept the defaults

In pictures: